1,026 research outputs found
Molecular Dynamics Simulations of Lead and Lithium in Liquid Phase
Pb17Li is today a reference breeder material in diverse fusion R&D programs worldwide. Extracting dynamic and structural properties of liquid LiPb mixtures via molecular dynamics simulations, represent a crucial step for multiscale modeling efforts in order to understand the suitability of this compound for future Nuclear Fusion technologies. At present a Li-Pb cross potential is not available in the literature. Here we present our first results on the validation of two semi-empirical potentials for Li and Pb in liquid phase. Our results represent the establishment of a solid base as a previous but crucial step to implement a LiPb cross potential. Structural and thermodynamical analyses confirm that the implemented potentials for Li and Pb are realistic to simulate both elements in the liquid phase
Experimental performance of a novel scraped surface heat exchanger for latent energy storage for domestic hot water generation
In this work, a novel design of a real scale Scraped Surface Heat Exchanger (SSHE) for solar LTES has been developed and experimentally tested. The main issue in PCM heat exchangers is the growth of a solid layer at the heat transfer walls during the latent energy extraction/discharging, that lowers heat transfer. The removal of the solidified PCM through scraping increases the heat transfer rate with nearly constant heat flux. Those characteristics make it suitable for domestic hot water generation. Discharging tests have been performed in scraping and no scraping modes (SM and nSM). The heat release rate in SM has shown to be between two and three times higher than in nSM. Moreover, in SM there is a complete extraction of the available latent energy (11.9 MJ) in a short period, compared to nSM. Additionally, a performance comparison between the developed SSHE and those available in open literature has been done. The results of heat release density (4 kW/m2) and overall heat transfer coefficient (1000 W/m2K) have shown similar values, though the scraping mechanism, the rotational speed, the size and their energy capacity are different. The developed design is an appropriate technology to increase the efficiency in solar LTES.The authors gratefully acknowledge to European Regional Development Fund and Ministerio de Ciencia e InnovaciĂłn - Agencia Estatal de InvestigaciĂłn for the financial support of the project ALTES: âActive Latent Thermal Energy Storageâ, Ref. PGC2018-100864-B-C21. We are also grateful to the company Outheway for the technical support in the design and manufacturing of scraper rotative heat exchanger. The present publication was first presented at the 16th Conference on Sustainable Development of Energy, Water and Environment Systems SDEWES conference, Dubrovnik, Croatia, 10â15 October 2021
Accelerated testing methods to analyse long term stability of a Phase Change Material under the combined effect of shear stress and thermal cycling
The long-term stability of a Phase Change Material (PCM) is a key point for its selection in energy storage devices. This work studies the suitability of a commercial paraffin wax in an active scraped surface heat exchanger for solar energy storage purposes. In these devices, the continuous scraping of inner walls during solidification removes PCM and increases the released heat. Hence, the PCM is affected by a high level of shear stress. In order to study a potential degradation of the paraffin, a novel accelerated procedure has been designed for obtaining samples with a different number of thermal and scraping cycles. The procedure allows to evaluate the effect of shear stresses, thermal cycles and their combined effects separately. Up to 3000 cycles have been generated, which accounts for around 8 years of continuous daily work in the heat exchanger. The measurements through Differential Scanning Calorimetry, rheometry and thermal conductivity analysis have shown that neither the thermal nor the scraping cycling have a significant impact on the paraffin thermo-physical properties. According to the findings reported in this work, paraffin wax RT44HC can be successfully used in scraped surface heat exchangers. It is expected that other commercial paraffins would be also suitable since most of them share the fact of being blends of alkanes and other hydrocarbons.The authors gratefully acknowledge to European Regional Development Fund and Ministerio de Ciencia e InnovaciĂłn - Agencia Estatal de InvestigaciĂłn for the financial support of the project ALTES: âActive Latent Thermal Energy Storageâ, Ref. PGC2018-100864-B-C21
Development of Magnetostrictive Transducer Prototype for Blockage Detection on Molten Salt Pipes
In solar thermal power plants molten salt is often used to store and transport the energy that is collected during the day. The external pipe temperature is measured to activate an electric heating system if the temperature approaches the melting point. However, salt solidification cannot be completely excluded from the plant management. Once occurred, the location of a salt blockage is very complex due to the high temperature of the pipe. Therefore, when this problem arises, power plants have to stop production with the consequences in time and cost that this entails. Electro-magnetic acoustic transducers can be used as non-destructive testing systems for this application. A method for salt blockage detection is proposed that is applicable in straight sections of pipes by employing torsional guided waves that are generated with magnetostrictive transducers. The present paper deals with the transducer conception and the design of the power supply to activate it. Two alternatives are proposed and compared to determine the improvement in the amplitude/noise ratio. Finally, the experimental results show the performance of the equipment in a small prototype, thus validating the technique presented
New simulations to qualify eutectic lithium-lead as breeder material
Pb17Li is today a reference breeder material in diverse fusion R&D programs worldwide. One of the main issues is the problem of liquid metals breeder blanket behavior. The knowledge of eutectic properties like optimal composition, physical and thermodynamic behavior or diffusion coefficients of Tritium are extremely necessary for current designs. In particular, the knowledge of the function linking the tritium concentration dissolved in liquid materials with the tritium partial pressure at a liquid/gas interface in equilibrium, CT =f(PT ), is of basic importance because it directly impacts all functional properties of a blanket determining: tritium inventory, tritium permeation rate and tritium extraction efficiency. Nowadays, understanding the structure and behavior of this compound is a real goal in fusion engineering and materials science. Atomistic simulations of liquids can provide much information; not only supplementing experimental data, but providing new tests of theories and ideas, making specific predictions that require experimental tests, and ultimately helping to a deeper understandin
Macroeconomic uncertainty : measurement and impact on the Spanish economy
ArtĂculo de revistaThis article characterises the level of uncertainty in the Spanish economy. Various indicators are analysed, distinguishing their source: financial market volatility, degree of disagreement between agents on the economic situation and economic policy uncertainty. Aggregate uncertainty in the Spanish economy increased in 2016, although it remained at levels below the average for the 2008-2013 recession. The changes in uncertainty captured by financial indicators are shown to have a higher impact on economic activity, and particularly on investment. Finally, it is illustrated how a significant part of the macroeconomic effect of the heightened uncertainty in the past year originated outside the Spanish econom
Molecular dynamics simulations of lead and lithium in liquid phase
Pb17Li is today a reference breeder material in diverse fusion R&D programs worldwide. Extracting dynamic and structural properties of liquid LiPb mixtures via molecular dynamics simulations, represent a crucial step for multiscale modeling efforts in order to understand the suitability of this compound for future Nuclear Fusion technologies. At present a Li-Pb cross potential is not available in the literature. Here we present our first results on the validation of two semi-empirical potentials for Li and Pb in liquid phase. Our results represent the establishment of a solid base as a previous but crucial step to implement a LiPb cross potential. Structural and thermodynamical analyses confirm that the implemented potentials for Li and Pb are realistic to simulate both elements in the liquid phase
Validation of a new methodological approach for the selection of wire-coil inserts in thermal equipment
The use of wire-coils is especially relevant at low Reynolds numbers (below the critical number to turbulent flow
in smooth tubes) according to its inherent positive features such as the advance of transition onset and, if they
present suitable geometric characteristics, the establishment of an extended transitional flow in a critical Reynolds number interval [ReCL â ReCT ], with a predictable friction coefficient and Nusselt number. This paper
presents the experimental validation of a new methodology based on the evaluation of a non-dimensional geometry-based parameter: the TSP (Transition Shape Parameter) that allows to predict the friction coefficient
evolution with wire-coil inserts and enables to compute the extension of the transitional flow region. The close
relationship between hydraulic and thermal performance of wire-coil inserts makes this methodology a valuable
tool for selecting the most appropriate wire-coil geometry for a given tubular heat exchanger. It is observed that
to promote an increase in heat transfer, the value of the ReCL of the wire coil must be less than the operating
Reynolds number range of the equipment. Thus, the ReCL â ReCT interval of the insert should fall into this range.
In order to validate the methodological approach, an application to harp-type solar thermal collectors with
typical Reynolds number range [40â6000] is presented. Four representative wire-coils, with a wide geometrical
range characterized by TSP values of 759, 196, 35.3 and 3.1 (exhibiting significant differentiated behaviours in
their friction factor curves and critical Reynolds numbers) were inserted inside the risers of a modified solar
collector and experimentally tested at laboratory conditions. Static temperature at different locations at the
absorber plate, and pressure drop were measured to obtain friction factor and Nusselt number inside riser
covering the laminar, transitional and low-turbulent regions.
For a general application with friction factor constraints the most suitable wire-coil geometry is the TSPW02 =
196 with a range of critical Reynolds number of ReCL = 663 and ReCT = 2286 and Nuw02/Nus = 2.21 for
Re = [300 â 3000] with f w02/fs = 3, 82. However, for the case study presented (a harp-type solar collector) it is
feasible to insert the third wire-coil geometry TSPW03 = 35.3 due to its early transition, with a range of critical
Reynolds number of ReCL = 364 and ReCT = 2324, and Nuw/Nus = 1.35 for Re = 300 with a high friction factor
augmentation f w03/fs = 18.84. This geometry also promotes the highest absorber temperature reduction. The
greatest temperature reduction is observed in the range of Reynolds numbers [700â2000], reaching approximately 6 âŠC, which represents approximately 15 %The authors gratefully acknowledge to European Regional Development Fund and Ministerio de Ciencia e InnovaciĂłn - Agencia Estatal de InvestigaciĂłn for the financial support of the project ALTES: âActive Latent Thermal Energy Storageâ, Ref. PGC2018-100864-B-C21
Liquid lead and Lithium. A Comprehensive molecular dynamics study
Pb17Li is today a reference breeder material in diverse fusion R&D programs worldwide. One of the main issues in these programs is the problem of liquid metals breeder blanket behavior. Structural material of the blanket should meet high requirements because of extreme operating conditions. Therefore the knowledge of eutectic properties like optimal composition, physical and thermodynamic behavior or diffusion coefficients of Tritium are extremely necessary for current designs. In particular, the knowledge of the function linking the tritium concentration dissolved in liquid materials with the tritium partial pressure at a liquid/gas interface in equilibrium, CT=f(PT), is of basic importance because it directly impacts all functional properties of a blanket determining: tritium inventory, tritium permeation rate and tritium extraction efficiency. Nowadays, understanding the structure and behavior of this compound is a real goal in fusion engineering and materials science. Simulations of liquids can provide much information to the community; not only supplementing experimental data, but providing new tests of theories and ideas, making specific predictions that require experimental tests, and ultimately helping to lead to the deeper understanding and better predictive behavior
Measuring economic and economic policy uncertainty, and their macroeconomic effects: the case of Spain
En este documento proporcionamos nueva evidencia acerca del impacto de la incertidumbre sobre la actividad econĂłmica. Para ello construimos, utilizamos y desarrollamos un conjunto amplio de indicadores sobre la incertidumbre econĂłmica y sobre las polĂticas econĂłmicas, para el caso de la economĂa española. Las medidas se agrupan en tres bloques: i) volatilidad de los mercados financierosii) desacuerdo entre los agentes econĂłmicos, y iii) incertidumbre sobre las polĂticas econĂłmicas. Los aumentos inesperados de la incertidumbre (perturbaciones asociadas a los indicadores) afectan negativamente al crecimiento econĂłmico, medido por el crecimiento del PIB real, en particular las de los bloques i) y iii). AdemĂĄs, en este trabajo se muestra que las perturbaciones en las medidas de incertidumbre sobre las polĂticas econĂłmica y financiera producen efectos negativos significativos en el consumo privado. Finalmente, la respuesta de la inversiĂłn en equipo es mĂĄs pronunciada en el corto plazo, pero presenta un efecto menos persistenteWe provide additional evidence on the relationship between uncertainty and economic activity. For this purpose, we gather and construct a wide range of proxy indicators of economic and economic policy uncertainty from Spain. We distinguish between the relative merits of different types of measures based on: (i) the volatility of financial markets(ii) economic analystsâ disagreement(iii) economic policy uncertainty. We show that the first and the third block of measures are the most relevant to grasp the negative effects of unexpected changes in uncertainty on aggregate economic developments, as measured by real GDP. In addition, we find that economic policy uncertainty and financial uncertainty shocks produce visible negative effects on private consumption. The negative responses on capital goods investments are initially bigger in magnitude but vanish more quickl
- âŠ