Heat transfer enhancement using nanofluids in the compression exchanger in a solar Stirling engine

In this paper a improvement in the heat exchange of a solar Stirling engine during the compression phase was studied. The viability of using nanoparticles as ceramic oxide (Al2O3 in water) at different concentrations instead of conventional refrigerants (water or air) was evaluated. Since these systems could behave as non- Newtonian fluids the dynamic viscosity was measured, as well as other thermophysical properties. The results showed that the convective heat transfer coefficient could raise one order of magnitude respect to the conventional heat transfer fluids at moderately volume fractions (over 0.15).Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tec

Characterization and thermophysical properties of rutile and alumina nanofluids

The characterization in relation to shape and particle size of alumina and rutile suspensions was performed. The intrinsic viscosity exhibited the presence of nonspherical aggregates in both suspensions although TEM images showed non monodisperse spherical shape of alumina particles. DLS indicated the existence of particle aggregates for both systems. In all cases, the increase in thermal conductivity with respect to the base fluid is verified. The thermal conductivities obtained experimentally were compared with three mathematical models, which yielded lower values than those measured. From rheological measurements and by means of the Peclet number defined in colloidal suspensions, values of thermal conductivity were also proposed.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tec

Advanced synchrotron studies of ye'elimite-based cement pastes

Synchrotron characterization techniques [1] are being used to study Portland-based cements and recently also CSA and related cements. A key property of these techniques is that they do not require sample preparation, so the microstructures of the pastes can be preserved. The classical application of synchrotron tools is powder diffraction used to determine the crystalline phase content evolution with hydration including the overall amorphous fraction. Furthermore, other most advanced techniques are being applied to ye'elimite-containing pastes such as i) Total Scattering Synchrotron Powder Diffraction (TS-SXPD), and ii) Ptychographic Synchrotron X-ray Computed Tomography (PSXCT). All these applications will be reviewed here. TS-SXPD data coupled with the Pair Distribution Function (PDF) analysis methodology [2] allows having a better insight about the nanocrystalline/amorphous atomic arrangements in the gels. It has been very recently shown that nanogibbsite with very small particles, 3nm, is the main constituent of ye'elimite-gypsum hydration paste [2]. Nanogibbsite particles being smaller than those originated from the hydration of monocalcium aluminate. In addition, PSXCT is a tomographic technique that profits from the partly coherent nature of the synchrotron beam to provide better (smaller) resolution, which can be lower than 100 nm. It also provides the mass densities if the chemical stoichiometries are known. This technique has been applied to ye'elimite hydration to determine the microstructure and chiefly the bulk densities of nanogibbsite [3]. The microstructure evolution at early age was also followed [4]. Figure 1 shows an example of a slide of the electron density tomogram for a ye'elimite paste at 8 days of hydration and the corresponding histogram for the full volume with all phases identified.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech.This work has been supported by Spanish MINECO through BIA2014-57658-C2 and BIA2017-82391-R, which are co-funded by FEDER

Quantitative disentanglement of nanocrystalline phases in cement pastes by synchrotron ptychographic X-ray tomography

Mortars and concretes are ubiquitous materials with very complex hierarchical microstructures. To fully understand their main properties and to decrease their CO2 footprint, a sound description of their spatially resolved mineralogy is necessary. Developing this knowledge is very challenging as about half of the volume of hydrated cement is a nanocrystalline component, calcium silicate hydrate (C-S-H) gel. Furthermore, other poorly crystalline phases (e.g. iron siliceous hydrogarnet or silica oxide) may coexist, which are even more difficult to characterize. Traditional spatially resolved techniques such as electron microscopy involve complex sample preparation steps that often lead to artefacts (e.g. dehydration and microstructural changes). Here, synchrotron ptychographic tomography has been used to obtain spatially resolved information on three unaltered representative samples: neat Portland paste, Portland–calcite and Portland–fly-ash blend pastes with a spatial resolution below 100 nm in samples with a volume of up to 5 x 104 mm3. For the neat Portland paste, the ptychotomographic study gave densities of 2.11 and 2.52 g cm -3 and a content of 41.1 and 6.4 vol% for nanocrystalline C-S-H gel and poorly crystalline iron siliceous hydrogarnet, respectively. Furthermore, the spatially resolved volumetric mass-density information has allowed characterization of inner-product and outer-product C-S-H gels. The average density of the inner-product C-S-H is smaller than that of the outer product and its variability is larger. Full characterization of the pastes, including segmentation of the different components, is reported and the contents are compared with the results obtained by thermodynamic modelling.This work has been supported by MINECO through BIA2014-57658 and BIA2017-82391-R research grants, which are cofunded by FEDER. Instrumentation development was supported by SNF (R’EQUIP, No. 145056,‘OMNY’) and the Competence Centre for Materials Science and Technology (CCMX) of the ETH-Board, Switzerland

Applications of synchrotron x-ray powder diffraction in hydrated cements: high-resolution and high-pressure studies

The main aim of this study is to apply synchrotron radiation techniques for the study of hydrated cement pastes. In particular, the tetracalcium aluminoferrite phase, C4AF in cement nomenclature, is the major iron-containing phase in Ordinary Portland Cement (OPC) and in iron rich belite calcium sulfoaluminate cements. In a first study, the hydration mechanism of pure tetracalcium aluminoferrite phase with water-to-solid ratio of 1.0 has been investigated by HR-SXRPD (high resolution synchrotron X-ray powder diffraction). C4AF in the presence of water hydrates to form mainly an iron-containing hydrogarnet-type (katoite) phase, C3A0.84F0.16H6, as single crystalline phase. Its crystal structure and stoichiometry were determined by the Rietveld method and the final disagreement factors were RWP=8.1% and RF=4.8% [1]. As the iron content in the product is lower than that in C4AF, it is assumed that part of the iron also goes to an amorphous iron rich gel, like the hydrated alumina-type gel, as hydration proceeds. Further results from the high-resolution study will be discussed. In a second study, the behavior of pure and iron-containing katoites (C3AH6 and C3A0.84F0.16H6) under pressure have been analyzed by SXRPD using a diamond anvil cell (DAC) and then their bulk moduli were determined. The role of the pressure transmitting medium (PTM) has also been studied. In this case, silicone oil as well as methanol/ethanol mixtures have been used as PTM. Some “new peaks” were detected in the pattern for C3A0.84F0.16H6 as pressure increases, when using ethanol/methanol as PTM. These new peaks were still present at ambient pressure after releasing the applied pressure. They may correspond to crystalline nordstrandite or doyleite from the crystallization of amorphous aluminium hydroxide. The results from the high-pressure study will also be discussed.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech. Acknowledgments: We thank CELLS-ALBA (Barcelona, Spain) for providing synchrotron beam time. We also thank the financial support by BIA2014-57658-C2-1-R and BIA2014-57658-C2-2-R (FEDER)

In-situ hydration studies of ye’elemite at early ages for understanding eco-cement performances'

Póster; ALBA User Meeting and VI AUSE Conferenc

Rheological study of the aggregation state of alumina nanofluids

Se adjunta una comunicación, aunque se han publicado tres comunicaciones más.The presence of alumina solid particles in aqueous phase induces a change in the viscosity of the suspension from Newtonian to non- Newtonian flow. Besides, the presence of solid particles is adequate for the use as a heat exchanger fluid. The effect of nanoparticle size on thermal properties of nanofluids is still today a question, which is far from being answered. In this respect, the results reported in the literature are contradictory [1], probably due to the formation of aggregates when particles are dispersed in the liquid phase. Regarding to the nanoparticle shape influence in thermal conductivity, cylinders and spheres have been considered as the more effective in heat transfer. Spherical nanoparticles of alumina, which is one of the most investigated nanofluid, dispersed in water were used in this study. TEM images showed a mean average diameter of 50 nm. However, DLS measurements showed monodispersed particles of 260 nm. Very recently [2], the relationship between shear rheology and aggregation state of suspensions has been reviewed. Mechanical and physical properties of the resultant materials depend on shape, size and size distribution, which are considered determining parameters in the formation of particle aggregates. The steady shear flow (figure 1) has shown that these clusters, when they are at rest, are formed by highly branched aggregates that erode when shear rate increases, until a suspension of individual particles is achieved. These results are in good agreement with the intrinsic viscosity obtained by Money and Krieger-Dougherty models. In both cases, these values are far from the 2.5 corresponding to spherical particles. The temperature effects were also taken into account.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

La masacre de Mapiripan en el marco de los derechos humanos internacionales.

Los Derechos Humanos amparados por las Constituciones de cada uno de los países que en el mundo la tienen, han sido sometidos a violación o a situaciones que dejan las promulgaciones y normas que sirven de soporte en tela de juicio. Los países cuando son marcados por los actos de violencia que como el caso de la masacre ocurrida en el municipio de Mapiripán, Meta, departamento del sur de Colombia, a mediados del año 1997, a manos del grupo ilegal identificado con la sigla AUC (equivalente a Autodefensas Unidas de Colombia), dejan en el banquillo de las acusaciones y responsabilidades a las fuerzas regulares del Estado, como así lo estableció la Corte Interamericana de Derechos Humanos mediante Sentencia C-15/2005, asignando   la culpabilidad del Estado colombiano, por colaboración de los miembros del ejército nacional, con quienes perpetraron y ejecutaron la masacre..En este artículo que constituye uno de los principales resultados de un estudio detallado de los aspectos que establecen la responsabilidad del Estado frente a la masacre de Mapiripan, se orientó por los siguientes objetivos: Determinar la responsabilidad del Estado frente a la masacre de Manirían; analizar el cumplimiento de la Corte Interamericana en los sucesos de Mapiripan Vs. Colombia; Identificar en la Sentencia emitida por la Corte Interamericana las sanciones y disposiciones ordenadas al Estado colombiano como resultado de la masacre de Mapiripan; establecer las acciones implementadas por el Estado colombiano para dar cumplimiento a las sanciones emitidas por la Corte Interamericana de Derechos humanos para que los afectados reciban una reparación adecuada por las violaciones cometidas; dar a conocer las medidas necesarias para evitar que hechos similares vuelvan a cometerse, de conformidad con el deber de prevención y garantía de los derechos fundamentales reconocidos en la Convención Americana

Modeling, monitoring, and diagnosis of complex systems with high-dimensional streaming data

With the development of technology, sensing systems became ubiquitous. As a result, a wide variety of complex systems are continuously monitored by hundreds of sensors collecting large volumes of rich data. Learning the structure of complex systems, from sensing data, provides unique opportunities for real-time process monitoring and for accurate fault diagnosis in a wide range of applications. This dissertation presents new methodologies to analyze the high-dimensional data collected by sensors to learn the interactions between different entities in complex systems for system monitoring and diagnosis.Ph.D