Contribuciones de la dialéctica a la organización del conocimiento

Knowledge organization, and its nurturing scientific disciplines, have been built on objectivism, a perspective rooted in positivism on which the Belgian found-ing fathers of Information Science developed their theories, and which has been continued through func-tionalism, the philosophical basement that holds together the technicist paradigm from which the problems of its domain are nowadays usually described or solved. However, operating such complex symbolic and discursive materials as knowledge, experience or memory —especially through their footprints and records (exo-memory) in the massive digital networks— requires studies carried out from sensible ethical, cultural and political positions. Dialectical exploration does not only provides essential clues to help us to understand some of the most decisive knowledge organization operations as highly mediated hermeneutics, but also provides us with the tools to ensure pluralism and democracy in the subjects and discourses that deserve it. The digital space offers new opportunities for diversity, but also an unprecedented threat of unification of cultures, democratic positions and dissent. Installing a dialectical consciousness into the core of knowledge organization and memory research and practice, as claimed by this article, will contribute to the protection and promotion of basic human rights through the regulated dialogue among the different and legitimate positions.La organización del conocimiento, y las disciplinas científicas matrices que la nutren, se ha cimentado en el objetivismo, una concepción arraigada en el positivismo que fundamentara a los  fundadores belgas y prosiguiera con el funcionalismo que sostiene el paradigma tecnicista desde el que se describen o resuelven los problemas derivados de su objeto de estudio. Sin embargo, operar con materiales simbólicos y discursivos tan complejos como el conocimiento, la experiencia o la memoria, especialmente a través de sus inscripciones y registros (exomemoria) en redes digitales masivas, precisa estudios desde posiciones política, ética y culturalmente sensibles. La exploración de la dialéctica no solo aporta claves esenciales para entender ciertas operaciones decisivas de la organización del conocimiento como acciones hermenéuticas altamente mediadas sino que también ofrece los instrumentos que garantizan el pluralismo y la democracia en las temáticas y discursos que lo merecen. El espacio digital ofrece nuevas oportunidades a la diversidad pero también una amenaza de unificación sin precedentes para las culturas, la democracia y el disenso. La instalación de una conciencia dialéctica en la investigación y las prácticas de organización del conocimiento y de la memoria, como pretende este artículo, contribuye a la protección y promoción de derechos humanos fundamentales mediante el diálogo regulado entre distintas y legítimas posiciones

Fully coupled TFM-DEM simulations to study the motion of fuel particles in a fluidized bed

In the present work, novel numerical simulations using a hybrid model are carried out to study the motion of objects, representing fuel particles, in a pseudo-2D fluidized bed. The hybrid model combines the continuum treatment of the gas phase with the possibility to treat different solid phases either as continuum, or discrete. In the present case, both the gas and the dense phase of the bed are modelled as continuum phases, as typically done in two-fluid model simulations, whereas fuel particles are simulated as discrete entities whose movement affects, and can be affected by the dense phase motion (i.e. fully coupled TFM-DEM simulations). The results obtained from the model are qualitatively and quantitatively compared with reported experimental findings available in the literature. Firstly, the motion of the fuel particle with regards to the bubble phase and dense phase is proved to be realistic. Secondly, the location probability of the particle in the simulated bed is calculated and compared with the experimental data. Then, the ballistic path followed by the particle in the freeboard is also compared with experimental measurements. These results show good agreement between experiments and simulation. The numerical results reflect the same behaviour during the ascending and descending motion of the fuel particles as that observed in the experiments. The results also show that the most probable locations of the particles predicted by the simulations are consistent with the experimental findings, both inside the fluidized bed and in the freeboard. Overall, the hybrid model tested shows quite promising results, which indicates the potential usability of the model.This work has been partially funded by the Spanish Government (Project DPI2009-10518) and the Autonomous Community of Madrid (Project S2009/ENE-1660).Publicad

Pyrolysis of sewage sludge in a fixed and a bubbling fluidized bed - Estimation and experimental validation of the pyrolysis time

Pyrolysis of sewage sludge was studied experimentally in a stainless-steel reactor operated as a fixed or fluidized bed. A novel measuring technique, consisting of measuring the mass of the whole reactor and the sample on a scale, was applied. The scale was capable of measuring the whole mass of the reactor with enough accuracy to detect the mass released by the sewage sludge sample during its pyrolysis. This original measuring technique permitted the measurement of the evolution over time of the mass of sewage sludge supplied to the bed in batch during its pyrolysis while moving freely in the bed. From the measurement of the mass of the solid residue remaining in the reactor, the pyrolysis time of the sewage sludge sample can be obtained accurately for each operating condition. Different operating conditions were selected to analyze the evolution with time of the sample mass during the pyrolysis process, including the bed temperature and the velocity of the Nitrogen used as inert gas. An increase of the velocity of Nitrogen from that of a fixed bed (0.8U(m)) to that of a low velocity bubbling fluidized bed (2.5U(mf)) accelerates remarkably the pyrolysis process, i.e. reduces the pyrolysis time, however increasing the Nitrogen velocity further has a slight effect on the characteristic velocity of the pyrolysis process. The pyrolysis process of sewage sludge can also be accelerated by increasing the bed temperature, even though the effect of the temperature is lower than that of the Nitrogen velocity. Furthermore, a mathematical model based on a first order apparent kinetics for the pyrolysis of sewage sludge was proposed. The model was employed to estimate the pyrolysis time for each operating condition, obtaining a proper agreement with the experimental measurements.The authors gratefully acknowledge the financial support provided by Fundación Iberdrola under the program "Programa de Ayudas a la Investigación en Energía y Medioambiente"

Optimization of the feeding ports location in a fluidized bed combustor based on Monte Carlo simulations of fuel particles motion

A Monte Carlo model was proposed to characterize the fuel particles motion in a large-scale fluidized bed. The model describes the global motion of a fuel particle with a proper circulation throughout the bed, analyzing its behavior both in the freeboard and inside the bed. The model was validated with experimental results of the lateral mixing of fuel particles in a large-scale fluidized bed reported in the literature. The lateral displacement of the fuel particles and the residence time, both in the freeboard and inside the bed, were obtained from the model. From those data the lateral dispersion coefficient of the fuel particle was determined. The influence of the operational conditions on the lateral dispersion coefficient and on the maximum lateral distance reached by a fuel particle for different residence times in the bed was also analyzed. Finally, an optimal distance between feeding ports to ensure suitable fuel dispersion was obtained.This work has been partially supported by the National Energy Program of Spanish Government (DPI2009-10518 MICINN) and CARDENER-CM (S2009ENE-1660).Publicad

Solid – Liquid separation of dairy manure: distribution of components and methane production

Chemical treatment and screening can be an effective technique for separation of dairy cattle manure into a liquid fraction (LF) and a nutrient-rich solid fraction (SF). The optimum loading of a strong cationic polyacrylamide was found to be 43.9 g kg−1 of dry excreta. The separated SF contained 29.1% of the initial mass present in the manure and the chemicals added. The Volatile Solids (VS)/Total Solids (TS) ratio, which was 0.78 for the manure, rose to 0.82 for the SF and decreased to 0.63 in the LF. Furthermore, the SF retained 76.1, 79.9, 59.4 and 87.4% of TS, VS, Total Kjeldahl Nitrogen and Total Phosphorus, respectively. In the LF, the ratio of filtrate chemical oxygen demand (CODfiltrate) and COD due to volatile fatty acids (CODVFA) in relation to total COD (CODT) were 0.86 and 0.76, respectively. The percentage of anaerobically biodegradable chemical oxygen demand (CODBD) for the LF was 83.0%. Treatment of the LF in high loading anaerobic reactors would be possible due to these COD characteristics. Specific methane production in terms of VS for the separated LF was 0.580 m3 kg−1. For dairy manure and SF, it was 0.320 and 0.258 m3 kg−1, respectivel

Experimental study on the motion of solids around an isolated bubble rising in a vertically vibrated fluidized bed

The motion of solids around isolated bubbles rising in a vertically vibrated pseudo-2D bed is experimentally studied in this work by combining Digital Image Analysis (DIA) and Particle Image Velocimetry (PIV). The bed material is Geldart B spherical particles. Different vibration amplitudes and frequencies are applied to the bed vessel while the bed is fluidized with air at minimum fludization conditions and isolated bubbles are sequentially injected in the bed. An averaging of bubbles method is presented and used to statistically characterize the average motion of solids around the bubbles. The results show that the presence of a bubble in the system perturbs the cyclic compression and expansion behavior of the bed bulk and, in particular, influences the velocity of the expansion wave front traveling upwards the bed. Analogously, the motion of solids around the bubble and, specially, in the bubble wake region, are strongly affected by the cyclic compression and expansion of the bed bulk. However, direct comparisons of the experimental results with the Davidson & Harrison potential flow model reveal that this model is still applicable for the prediction of the solids velocity around the bubble in a vertically vibrated fluidized bed

Thermo-economic optimization of a novel confined thermal energy storage system based on granular material

Concentrated solar power is a suitable technology for production of green electricity. However, to attain a uniform electricity production, concentrated solar power should be coupled with large Thermal Energy Storage (TES) systems. Among the different technologies of TES systems, storage of sensible heat in granular material is widely used due to its simple operation. These TES systems store energy as an increase of temperature of a large mass of small solid particles, through which a fluid circulates exchanging heat. TES systems are typically operated in a fixed bed regime, maximizing their exergy output, thus limiting the maximum allowable velocity of the fluid flow. In this work, a novel confined bed is proposed to mechanically prevent the motion of the solid particles conforming the TES system even for high fluid velocities, to guarantee that the exhaust temperature of the fluid is maximum during a discharge process. In this novel confined bed, a thermocline evolves from bottom to top of the system, separating the low and high temperature of the bed during the discharge process. An analytical model was applied to describe the evolution of the thermocline and the effect of the different operating parameters on the thermocline thickness. The effect of the thermocline thickness was combined with a thermo-economic analysis of a confined bed TES system proposed for a case of study. The new confined bed here proposed was optimized considering thermodynamics aspects, namely the fluid exergy increment in the bed, and economic factors, specifically the total investment cost of the TES system. The optimization resulted in low values of the fluid velocity, between 0.2 and 0.4 m/s, but still higher than the minimum fluidization velocity of sand particles of 750 mum, justifying the requirement of a confined bed, and low bed aspect ratios, between 0.25 and 0.9, to prevent excessively high fluid pressure drops. However, the bed aspect ratio increases significantly for higher granular material particle sizes, up to a ratio of bed height to diameter of 3 for a particle size of 10 mm and a TES demand time of 6 h.This research was funded by the Spanish Government under the project STORESOL, reference number PID2019-109224RA-100. Eduardo Cano-Pleite also acknowledges support from the CONEX-Plus program funded by Universidad Carlos III de Madrid and the European Union's Horizon 2020 program under the Marie Sklodowska-Curie grant agreement No. 801538.Publicad

An experimental evaluation of broadband spatial IA for uncoordinated MIMO-OFDM systems

In this paper we present an experimental study on the performance of spatial Interference Alignment (IA) in broadband indoor wireless local area network scenarios that use Orthogonal Frequency Division Multiplexing (OFDM) according to the IEEE 802.11a physical-layer specifications. Experiments have been carried out using a wireless network testbed made up of six nodes equipped with Multiple-Input Multiple-Output (MIMO) radio interfaces. This setup allows the implementation of a 3-user MIMO interference channel. We have implemented different IA decoding schemes that operate either before or after the Fast Fourier Transform block. IA has been experimentally evaluated comparing both approaches to analyze its performance in synchronous and asynchronous transmissions. Our results indicate that spatial IA performs satisfactorily in practical broadband indoor scenarios in which wireless channels often exhibit relatively large coherence times.This work has been supported by the MINECO of Spain and Feder funds of the E.U. under grants CSD2008-00010 (COMONSENS project), TEC2013-47141-C4-R (RACHEL project) and FPU grant AP2010-21

Evaluating the accuracy of the Distributed Activation Energy Model for biomass devolatilization curves obtained at high heating rates

The characteristic parameters of devolatilization, the activation energy and the frequency factor, can be obtained following different experimental approaches. In the Distributed Activation Energy Model (DAEM), these parameters are derived from several TGA curves that are typically obtained for constant, low heating rate experiments. Then, the results are used to model high heating rate processes typical of industrial combustors. In this work, a wide range of heating rates were employed to obtain different TGA curves of the biomass pyrolysis, in order to analyse the validity of DAEM when extrapolating the kinetic parameters obtained for low heating rate curves used in the laboratory to higher heating rates present in industrial applications. The TGA curves of the biomass pyrolysis employed in DAEM were varied from low heating rates (around 10 K/min, values typically found in the literature on DAEM), to high heating rates (up to 200 K/min). The differences in the activation energy and the frequency factor obtained for different heating rates, were evaluated and the validity of the model was discussed. The results show differences between the activation energy and the frequency factor obtained using low and high heating rates during the TGA tests. Therefore, if an accurate approximation is required when extrapolating the data to high heating rates, the tests should be carried out at high heating rates.The authors would like to express appreciation to the BIOLAB experimental facilities and for the financial support from Projects DPI2009-10518 (MICINN) and CARDENER-CM (S2009ENE-1660).Publicad

Modeling the thin-layer drying process of Granny Smith apples: Application in an indirect solar dryer

The thin-layer drying kinetics of Granny Smith apples is determined by thermogravimetric analysis of the drying process at constant temperatures ranging from 20 degrees C to 50 degrees C, using intervals of 5 degrees C. The experimental drying curves obtained in the TGA were fitted to the Wang-Singh equation, which was found to describe precisely the drying process occurring at constant drying temperature. A novel model, capable of predicting the evolution of the moisture ratio of Granny Smith apples during the drying process with variable drying temperatures, was proposed. The model was validated with experimental TGA measurements of the drying of apples at variable temperatures, typical of solar drying, obtaining maximum deviations for the drying time less than 1.5%. Once validated, the model proposed was also applied to the drying of Granny Smith apples in an indirect solar dryer. The comparison of the model prediction with the experimental measurements of the drying of apples at variable drying conditions conducted in a lab-scale solar dryer showed a proper agreement, with low deviations (less than 10%) associated to the thermal inertia of the samples. (C) 2016 Elsevier Ltd. All rights reserved.The thermogravimetric analyses were conducted in the BIOLAB experimental facility (madrimasd.org, lab # 202), a laboratory financed under the infrastructures and lab network of the Madrid (Spain) Regional Governmen