Marangoni hydrodynamic motion and its potential technological application in reverse osmosis (RO) process for seawater desalination is discussed. The fundamental core idea in this note is the possibility to take advantage of the inherent concentration gradient in a RO process. It is well known that to run a RO process, it is necessary to apply a hydrodynamic pressure to overcome the osmotic pressure, however, by inducing a free-surface, e.g., a Leidenfrost surface, on the membrane wall, an additional hydrodynamic Marangoni stress could be generated, which, likewise than the osmotic pressure is driven by the concentration gradient but acting in the opposite direction, i.e., reducing the external hydraulic pressure to be applied. Utilizing a simplified geometrical and physical model, an analytical expression for the pressure reduction was derived. One important preliminary result in this work, is that the Marangoni stress can provide pressure against the osmotic pressure for membrane porous that are less than micrometric size.
Sustainability issues, as unwanted results of not fully respecting natural cycles, are widely recognized as wicked problems, which should not be thought of as problems to be solved, but rather as “conditions” to be managed, as if they were a chronic disease (Seager et al., 2011).
There exists a general agreement on the need to reform scientific expertise by developing new ways of knowledge production and decision-making able to cope with the challenges sustainability poses. In this sense, transdisciplinary aspects of sustainability are acknowledged as a transformational stream of sustainability science
Nowadays, hydropower plays an essential role in the energy market. Due to their fast response and regulation capacity, hydraulic turbines operate at off-design conditions with a high number of starts and stops. In this situation, dynamic loads and stresses over the structure are high, registering some failures over time, especially in the runner. Therefore, it is important to know the dynamic response of the runner while in operation, i.e., the natural frequencies, damping and mode shapes, in order to avoid resonance and fatigue problems. Detecting the natural frequencies of hydraulic turbine runners while in operation is challenging, because they are inaccessible structures strongly affected by their confinement in water. Strain gauges are used to measure the stresses of hydraulic turbine runners in operation during commissioning. However, in this paper, the feasibility of using them to detect the natural frequencies of hydraulic turbines runners while in operation is studied. For this purpose, a large Francis turbine runner (444 MW) was instrumented with several strain gauges at different positions. First, a complete experimental strain modal testing (SMT) of the runner in air was performed using the strain gauges and accelerometers. Then, the natural frequencies of the runner were estimated during operation by means of analyzing accurately transient events or rough operating conditions.
Hydropower plays a key role in the actual energy market due to its fast response and regulation capacity. In that way, hydraulic turbines are increasingly demanded to work at off-design conditions, where complex flow patterns and cavitation appear, especially in Francis turbines. The draft tube cavitation surge is a hydraulic phenomenon that appears in Francis turbines below and above its Best Efficiency Point (BEP). It is a low frequency phenomenon consisting of a vortex rope in the runner outlet and draft tube, which can become unstable when its frequency coincides with a natural frequency of the hydraulic circuit. At this situation, the output power can significantly swing, endangering the electrical grid stability. This study is focused on the detection of these instabilities in Francis turbines and their relationship with the output power swings. To do so, extensive experimental tests for different operating conditions have been carried out in a large prototype Francis turbine (444 MW of rated power) within the frame of the European Project Hyperbole (FP7-ENERGY-2013-1). Several sensors have been installed in the hydraulic circuit (pressure sensors in the draft tube, spiral casing, and penstock), in the rotating and static structures (vibration sensors, proximity probes, and strain gauges in the runner and in the shaft), as well as in the electrical side (output power, intensity, and voltage). Moreover, a numerical Finite Element Method (FEM) has been also used to relate the hydraulic excitation with the output power swing.
Pressure retarded osmosis (PRO) process and its significance for thermosyphon technology is discussed. In previous work the possibility to drive a thermosyphon by difference of densities from induced salinity gradients from evaporation at solar collectors with downward heat transfer was assessed. Nevertheless it was concluded that large evaporative areas or dilution with volatile compounds was mandatory. In this work it is shown that by taking advantage of the energy released during the spontaneous mixing of the low-concentration evaporative fraction and the high-salinity of the no-evaporated fraction which is generally referred as pressure-retarded osmosis (PRO) process, then the thermosyphon can runs with downward heat transfer (hot fluid flows down and cold fluid rises up) and using an evaporative surface area much more smaller and then eliminating the need for dilution with high volatile compounds.
El presente libro es fruto de la experiencia adquirida durante toda una carrera universitaria. Esta obra está diseñada para presentar los principios básicos de la Mecánica de Fluidos de una manera clara y muy sencilla. Muchos de los problemas que se exponen fueron, en su momento, problemas de examen de la asignatura. Asimismo, pretende ser un libro de repaso para quienes, precisen fijar determinados conceptos sobre la materia. Finalmente, se desea que esta obra sirva de apoyo a todas las escuelas de los países de habla hispana que imparten las diversas Ingenierías. Espero y deseo que este libro sea un instrumento útil de repaso de la temática presentada.
The global trend on energy integration and building efficiency is making both researchers
and building developers look for technical solutions to use facade surfaces for energy harvesting.
In this work, the assessment of the thermal performance of a double-skin facade (DSF) with a venetian
blind-type of structure used as a solar thermal collector by means of computational fluid dynamics
(CFD) is presented. A Venetian blind collector would allow for heat rejection/energy harvesting and
exterior views simultaneously and can be easily integrated into the DSF aesthetical design. For the
purposes of this study, the modeled facades (south, west, and east-oriented) were set to be located in
Barcelona (Spain), where large solar gains are a constant condition throughout the year, and such
large semi-transparent envelopes lead to interior over-heating in buildings, even during the winter.
For the studied facades, both the reductions in radiative heat gains entering the building and the heat
recovery in the Venetian blind collector were evaluated for a yearlong operation.
En este artículo se presenta el primer resultado del proyecto EDINSOST: un mapa de la competencia Sostenibilidad para el Grado de Ingeniería Informática, fácilmente adaptable a cualquier titulación de Grado en Ingeniería y a otras titulaciones superiores. El mapa ha sido desarrollado dentro del proyecto EDINSOST, cuyo objetivo es la formación de titulados capaces de liderar la resolución de los retos de nuestra sociedad mediante la integración de la formación en competencias en Sostenibilidad en el Sistema Universitario Español. Este mapa se ha adaptado con éxito a cinco grados en ingeniería (Informática, Eléctrica, Química, Mecánica y Diseño), un Grado en Ciencias Ambientales y un Grado en Administración y Dirección de
Egusquiza, M.; Egusquiza, E.; Valentin, D.; Valero, M.; Presas, A. Engineering failure analysis Vol. 81, p. 234-244 DOI: 10.1016/j.engfailanal.2017.06.048 Data de publicació: 2017-11 Article en revista
In this paper, an uncommon failure of a Pelton turbine has been analyzed. After the monitoring system detected a sudden increase in the vibration levels, the turbine was inspected. The inspection showed that a fragment of one bucket broke off during operation. Moreover there were several buckets with cracks, always located in the same side of the buckets. An analysis of the detached fragment revealed a fatigue problem.After the damage was found, the vibration signatures measured by the monitoring system before damage, with damage and after repair, were analyzed. Before damage occurred, an excessive axial vibration and the excitation of several natural frequencies of the turbine were detected in the measured vibration.In order to identify the origin of the problem the first task was to analyze the dynamic response of the turbine. A numerical model of the runner using the finite element method (FEM) was done. Experimental research using modal analysis techniques (EMA) was also carried out in the turbine runner. The results of the numerical model were compared with the experimental results obtained. With the validated numerical model natural frequencies and mode-shapes were determined and studied.The next step was to determine experimentally the influence of the mounting conditions on the runner dynamics and the transmissibility of the runner vibrations to the machine bearings where the monitoring sensors are located.From the results of this study it was concluded that the natural frequencies excited during machine operation had axial mode shapes indicating that axial forces were applied to the runner. In a Pelton turbine, this can only be produced by a misaligned jet.To determine the influence of a misaligned jet on the bucket stresses, the dynamic behavior of the runner was performed. The dynamic force of the water jet was applied to the runner bucket. The results showed that with a misaligned jet the dynamic stress distribution increases in one side of the bucket with a maximum stress located where the cracks appeared.
Many safety-critical hydraulic components in agricultural and other off-road mobile machinery experience static as well as time-varying loads, and obviously they undergo the latter during a major portion of their service life. Fatigue behaviour is, therefore, a key consideration in design and performance evaluation of hydraulic components.
The durability evaluation of components based experimental results obtained from field is time-consuming and expensive, so simpler approaches that include a limited number of component verification tests have become popular. A problem that arises when studying the fatigue behaviour of such components, with simpler approaches as mentioned, is the transferability of data from those limited number of verification tests, which provide real-life load histories (recorded data of load vs time that machine will experience repeatedly during service life), to be used in the accelerated test methods (laboratory environment) for validating the internal rated fatigue pressure (RFP) of components. The RFP is the pressure (component specification) which a component is verified to achieve, with a known probability, the rated life without failure.
Derived from the know-how and experimental background of the authors, the paper describes a simple procedure for the assessment of hydraulic components against fatigue based on the real-life load histories of a predetermined machine application using fatigue damage and life prediction rules. Conclusions are (1) that real-life load histories can essentially be reproduced, equivalently in terms of damage produced and life obtained, by constant amplitude fatigue tests and (2) that this method not only permits decide the design specification (pressure-life) of components already in serial production, but also of those components that are still in the design phase.
Cushioning is an important aspect in hydraulic cylinder performance. The piston has to be decelerated before it strikes the end cap in order to avoid stresses in the cylinder components and reduce vibration that can be transmitted to the machine. One of the least-studied methods is internal cushioning by grooves in the piston. In this method, the flow is throttled with adequately designed grooves when the piston reaches the outlet port position. The purpose of the present work is to present a method to estimate the pressure-drop coefficients for a certain design of piston grooves in order to provide a model to develop a dynamic system simulation of the cushion system. The method is based on a computational fluid dynamic simulation of flow through piston grooves to the outlet port for each piston’s static position. The results are compared with experimental measurements, and a correction, based on Reynolds number, is proposed. Good agreement, below 16%, was obtained for all the positions but particularly for the last grooves, for which the numerical result’s deviation to the experimental measurements was less than 10%. In general, the numerical simulation tended to underestimate the pressure drop for the first grooves and overestimate the calculation for the last grooves.
This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).
Sensorization of modern electro-hydraulic systems is one of the key technologies for system observability and controllability. Increasing needs for closed loop controls, high precision, power control and energy monitoring, diagnosis and safety concerns, ask for both pressure and flow acquisition in industrial and mobile applications. Pressure sensors need specific coupling systems for mounting, and both pipes and components must be modified to install pressure sensors. Traditional pressure sensors are related to mini-mess and to oil flow modification in the sensor area. Direct pressure measurement is often made using thin film sensors whose measurement principle is related to a strain measurement. Modern Silicon based technologies offer new solutions for a less invasive pressure measurement. Micro Electro-Mechanical Systems (MEMS) Technology is suitable to design new sensors for indirect pressure measurement. This paper present a new MEMS resonant sensor, for low strain measurement that can be successfully used to indirectly measure oil pressure acquiring component’s strain measurement.
The main goal of modern steering systems is to ensure the feeling of control whilst keeping an high safety level since steering is one of the most critical function of a mobile machine. In manifold mobile machines the architecture include priority valves that on one hand increase safety, on the other increase the energy demand. In the present work a conceptual study of a novel steering system is outlined. With this architecture some reduction of fuel consumption can be obtained avoiding flow supply in idle condition. The system is separated from the rest of the hydraulic system thus the priority valve is not necessary. The aim of the system is to have the same characteristics of a classical system (with steering unit), with a better energy behavior in idle regime. Several simulations will be analyzed with the aim of studying the steering performance with emphasis on the steering wheel control characteristics in both normal and emergency operation.
Consideration is given to the possibility to use changes in buoyancy as a negative reactivity feedback mechanism during temperature transients in heavy liquid metal fast reactors (HLMFRs). It is shown that by the proper use of heavy pellets in the fuel elements, fuel rods could be endowed with a passive self-ejection mechanism and then with a negative feedback. A first estimate of the feasibility of the mechanism is calculated by using a simplified geometry and model. If in addition, a neutron poison pellet is introduced in the bottom of the fuel, then when the fuel element is displaced upward by buoyancy force, the reactivity will be reduced not only by disassembly of the core but also by introducing the neutron poisson from the bottom. The use of induced buoyancy opens up the possibility of introducing greater amounts of actinides into the core, as well as providing a palliative solution to the problem of positive coolant temperature reactivity coefficients that could be featured by the HLMFRs.
Segalas, J.; De Eyto, A.; McMahon, M.; Joore, P.; Crul, M.; Wever, R.; Jimenez, A. European Roundtable for Sustainable Consumption and Production p. 80 Data de presentació: 2017-10-04 Presentació treball a congrés
The potential use of changes in buoyancy as a reactivity feedback mechanism during temperature transients in heavy liquid metal fast reactors (HLMFRs) is discussed. It is shown that with the use of ballast pellets (~15% volume fraction) introduced in combination with fuel pellets, fuel rods will be endowed with a reliable self-ejection mechanism that is able to compensate temperature transients. Utilizing a simplified model, an estimate of the negative reactivity insertion expected from this mechanism is derived. The use of ballast pellets opens up the possibility of introducing greater amounts of actinides into the core, as well as providing a solution to the classical problem of positive coolant temperature reactivity coefficients in fast reactors.
The trochoidal-gear technology has been growing in groundbreaking fields. Forthcoming applications are demanding to this technology a step forward in the conceiving stage of positive displacement machines. The compendium of the qualities and the inherent characteristics of
trochoidal-gear technology, especially towards the gerotor pump, together with scale/size factor and magnetic-driven transmission has led to the idea of a magnet-sleeve-sealed variable flow mini trochoidal-gear pump. From its original concept, to the last phase of the design development, the proof of concept, this new product will intend to overcome problems such as noise, vibration, maintenance, materials, and dimensions. The paper aims to show the technological path followed from the concept, design, and model, to the manufacture of the first prototype, where the theoretical and numerical approaches are not always directly reflected in the prototype performance results.
Early in the design process, from a standard-commercial sintered metal mini trochoidal-gear unit, fundamental characteristics and dimensional limitations have been evaluated becoming the strategic parameters that led to its configuration. The main technical challenge to confront is being sealed with non-exterior driveshaft, ensuring that the whole interior is filled and wetted with working fluid and helping the hydrodynamic film formation, the pumping effect, and the heat dissipation. Subsequently, the mini pump architecture, embodiment, methodology, materials, and manufacture are presented. The trend of applications of polymer composite materials and their benefits wanted to be examined with this new mini pump prototype, and a pure polyoxymethylene mini trochoidal-gear set has been designed and manufactured. Finally, both the sintered and the polymer trochoidal-gear units have been experimentally tested in an in-house full-instrumented mini test bench. Although the main goal of the presented work is the development of a new mini trochoidal-gear pump prototype rather than a numerical study, the results have been compared with numerical simulation. Subsequently, the prototype of the mini trochoidal-gear pump is a feasible proof of concept supported by functional indexes and the experimental results.
Sustainability and internationalization are key factors within educational programmes and institutions nowadays. Offering programmes that focus on these factors at undergraduate level has been a priority at the Schoolof Engineering of Vilanova i la Geltrú (EPSEVG), Barcelona , and since 2012, it has run the International Design Project Semester (IDPS) Erasmus mobility programme.
IDPS trains engineering design students by applying Project Based Learning in intercultural groups. The working language is English and the programme is designed for bachelor degree students in their 7th or 8th semester. The IDPS programme offered at the EPSEVG emphaises the indtroduction of competences in sustainability andhuman technology
Sustainability and internationalization are key factors within educational programmes and institutions nowadays. Offering programmes that focus on these factors at undergraduate level has been a priority at the Schoolof Engineering of Vilanova i la Geltrú (EPSEVG), Barcelona , and since 2012, it has run the International Design Project Semester (IDPS) Erasmus mobility programme.
IDPS trains engineering design students by applying Project Based Learning in intercultural groups. The working language is English and the programme is designed for bachelor degree students in their 7th or 8th semester. The IDPS programme offered at the EPSEVG emphaises the indtroduction of competences in sustainability andhuman technology.
The research Institute for Sustainability Science and Technology under the Masterdegree in Sustainability Science and Technology organises the course Action Reserach Workshop on Science and Technology for Sustainability (5 ECTS). The purpose of the course is to put together civil society organisations, local administrations, students and educators to collaboratively undertake responsible research, using transdisciplinary Action-Research methodologies through service learning.
The Research Institute for Sustainability Science and Technology under the Master degree in Sustainability Science and Technology organises the course Action Research Workshop on Science and Technology for Sustainability (5 ECTS). The purpose of the course is to put together civil society organisations, local administrations, students and educators to collaboratively undertake responsible research, using trandisciplinary Action-Research methodologies through service learning.
Until now mechanisms responsible for the observed deuterium enrichment in some planets or celestial bodies are tge resykt if serveral thermal (Jeans escape) as well as non-thermal escape mechanisms. In this work, we will conjecture the possible contribution from the solar wind interacting with the magnetic fields of the planet or celestial body. The most interesting feature of this hypothesis, is that the enrichment of deuterium is not due to the preferential escape of hydrogen from the atmosphere, but rather, the enrichment is generated by external injection of deuterium into the atmosphere with solar wind or galactic clouds as sources. The hypothesis also open the possibility that planets and celestial bodies may have been enriched with deuterium in the past when solar system passed through a galactic cloud. If so, there is speculative possibility of geological records where an abrupt enrichment of deuterium may disclose the transit of the solar system through such a galactic cloud in the past, an then a sort of "deuterium-age" could be suggested.
Consideration is given to the formation and collapse of supersaturated tropospheric cavities on Mars for dust vertical transportat extreme altitudes as a tentative mechanism explaining the martian march-2012 plume. It will be shown that if, during the night-time radiative cooling is exarcerbated by suspended dust surrounding a tropospheric parcel and then impeding heat flow from the surface into the parcel and if, additionally the parcel itself is devoid of condensation nuclei (dust aerosol on Mars) a supersaturated cavity might be generated. Then, with the first rays of sunlight in the morning -and the beginning of the daily dust activity, any dust incursion into the cavity driven by local winds, could trigger the condensation of the parcel and the subsequent vigorous prompt collapse of the cavity. Utilizing a simplified geometrical model, it is shown that the collapse and rebound of such tropospheric cavities could provide enough energy to lift dust well into the thermosphere and then a possible explanation to the extremely high-altitude plumes seen on Mars. The proposed hypothesis seems consistent with the high-altitude plume seen at Mars 2012 at Cimmeria region -and still unresolved, occurred at the Martian terminator (the day-night boundary) when the atmosphere could be coldest because has been without the heat of the sun for the longest time and the beginning of the dust activity driven by solar heating. Finally the possibility that the local strong magnetic field in Cimmeria region may have played a role in triggering the formation of the hypothesized supersaturated tropospheric cavity or "magnetocavity" was also discussed.
Consideration is given to the formation and collapse of supersaturated tropospheric cavities on Mars for dust vertical transport at extreme altitudes as a tentative mechanism explaining the martian march-2012 plume. It will be shown that if, during the night-time radiative cooling is exarcerbated by suspended dust surrounding a tropospheric parcel and then impeding heat flow from the surface into the parcel and if, additionally the parcel itself is devoid of condensation nuclei (dust aerosol on Mars) a supersaturated cavity might be generated. Then, with the first rays of sunlight in the morning -and the beginning of the daily dust activity, any dust incursion into the cavity driven by local winds, could trigger the condensation of the parcel and the subsequent vigorous prompt collapse of the cavity. Utilizing a simplified geometrical model, it is shown that the collapse and rebound of such tropospheric cavities could provide enough energy to lift dust well into the thermosphere and then a possible explanation to the extremely high-altitude plumes seen on Mars. The proposed hypothesis seems consistent with the high-altitude plume seen at Mars 2012 at Cimmeria region -and still unresolved, occurred at the Martian terminator (the day-night boundary) when the atmosphere could be coldest because has been without the heat of the sun for the longest time and the beginning of the dust activity driven by solar heating. Finally the possibility that the local strong magnetic field in Cimmeria region may have played a role in triggering the formation of the hypothesized supersaturated tropospheric cavity or "magnetocavity" was also discussed.
The possible role of magnetic anomalies on Mars in gravitational enhancement of separation of charged dust is considered. It is known that charges become spatially separated by differential transport and gravitational sedimentation because the charge polarity of particles od dust depends on the particle size - where smaller particles are negatively charged and larger particles are positively charged; thus smaller and predominantly negative charged particles populate higher regions of dust devils, and larger, positively charged particles fall to the ground. This study shows that gravitational separation could be enhanced by the presence of magnetic anomalies on Mars owing to the generation of a type of magnetobarrier that prevents gravitational settling of charged dust particles beyond a certain size threshold.
The basis of a novel method for seawater desalination is outlined. In this work, pressure-retarded osmosis (PRO) energy is obtained and used posteriorly for the reverse osmosis (RO) process for seawater desalination. Although PRO process coupled with an RO process has been studied in the past, however, in this work, there is a fundamental difference. Instead of bringing river or wastewaters with low salinity to the coast to be mixed with the seawater to run the PRO process, here is the seawater which is deliberately salinized. This technique has one important consequence, namely, that it is no longer required to be in places where rivers or wastewaters flow into the sea. This important difference eliminates this until now somehow paradoxical requirement if one considers that regions needing desalination are generally poor of water resources. On the other hand, it is not a coincidence that regions needing desalination plants are also regions with rich open salt deposits in the neighborhood; high evaporation, high concentration of salt deposits, and the need for freshwater are all of them directly correlated. Therefore, the idea proposed in the paper is consistent with the problem. The high evaporation in the region which is causing the need for desalination also is creating the solution to do this by using the salt deposits created. The economic feasibility of this method is preliminarily assessed in terms of the thermodynamic limits of extractable energy and then with the cost of the salt required to obtain this energy which is compared with the price from electrical grid. It was found that in order to reduce the amount of salt required for the process, and to make the cost of energy competitive, it is necessary to direct the hypersaline draw solution (draw solution) in a cyclic loop and to have the highest possible volume fraction for the nonsalinized solution (feed solution). Additional R&D is required to explore the possibilities of this concept.
Segalas, J.; De Eyto, A.; McMahon, M.; Joore, P.; Crul, M.; Wever, R.; Jimenez, A. International Conference on Engineering and Product Design Education p. 18 Data de presentació: 2017-09-07 Presentació treball a congrés
The basis of a novel method for passive solar water heating homologous to the thermosiphon but driven by induced salinity, which causes a fluid to circulate without the need for a mechanical pump and with inverse natural convection (downward heat transfer), is outlined. The brinesiphon, like the thermosiphon, operates by harnessing the tendency of a less dense fluid to rise above a denser fluid, resulting in fluid motion through a collector, but with two exceptions: first, the
buoyancy is controlled by induced salinity gradients rather than thermal gradients, and second, as a result, natural convection is in the opposite direction than that in the homologous thermosiphon concept; i.e., hot fluid flows down, and cold fluid rises. A brinesyphon may be more suitable for solar domestic water heating systems than the thermosiphon because the direction of flow allows downward transfer from a solar collector to a lower storage tank without any type of mechanical pumping system.
Presas, A.; Valentin, D.; Egusquiza, M.; Bossio, M.; Egusquiza, E.; Valero, M. International Symposium on Sensor Science p. 822- DOI: 10.3390/proceedings1080822 Data de presentació: 2017-09 Presentació treball a congrés
Nowadays, hydropower plants are of paramount importance for the integration of intermittent renewable energy sources in the power grid. In order to match the energy generated and consumed, Large Hydraulic Turbines have to work at off-design conditions, which may lead to dangerous unstable operating points involving the hydraulic, mechanical and electrical system. Under these conditions, the stability of the power grid and the safety of the powerplant itself can be compromised. For many Francis Turbines, one of these critical points, that usually limits the maximum output power, is the full load instability. Therefore, these machines usually work far away from this unstable point, reducing the effective operating range of the unit. In order to extend the operating range of the machine, working closer to this point with a reasonable safety margin, it is of paramount importance to monitor and to control relevant parameters of the unit, which have to be obtained with an accurate sensor acquisition strategy. In the frame of a large EU Project, field tests in a large Francis Turbine located in Canada (rated power 444 MW) have been performed. Many different sensors were used to monitor several working parameters of the unit for all its operating range. Particularly for these tests, more than 80 signals, including ten types of different sensors and several operating signals that define the operating point of the unit, were simultaneously acquired. The present study focuses on the optimization of the acquisition strategy, which includes type, number, location, acquisition frequency of the sensors and corresponding signal analysis to detect the full load instability and to prevent the unit from reaching this point. In this way, the operating limits of the unit can be more accurately defined and therefore the effective operating range increased.
Valentin, D.; Presas, A.; Bossio, M.; Egusquiza, M.; Egusquiza, E.; Valero, M. International Symposium on Sensor Science p. 821- DOI: 10.3390/proceedings1080821 Data de presentació: 2017-09 Presentació treball a congrés
Nowadays, hydropower plays an essential role in the energy market. Due to its fast response and regulation capacity, hydraulic turbines operate at off-design conditions with a high number of start and stops. In this situation, dynamic loads and stresses over the structure are high, documenting some failures over time, especially in the runner. Therefore, it is important to know the dynamic response of the runner under operation, i.e., natural frequencies, damping and mode-shapes, in order to avoid resonance and fatigue problems. The detection of natural frequencies of hydraulic turbine runners in operation is challenging because they are inaccessible structures strongly affected by the confinement in water. Strain gauges are used to calculate stresses of hydraulic turbine runners under operation. However, in this paper, the feasibility to use them to detect natural frequencies of hydraulic turbine runners under operation is studied. For this purpose, a large Francis turbine runner (444 MW) was instrumented with several strain gauges at different positions. First, a complete Experimental Modal Analysis (EMA) of the runner in air was performed using the strain gauges. Then, the natural frequencies of the runner were estimated during operation by means of analyzing accurately transient events or rough operating conditions.
We evaluated the hydrogeochemical characteristics of water from the old flooded Sierra Almagrera mines to determine the possible origin of its geothermal fluids, to establish a geological-geochemical model of the geothermal system, and evaluate the site’s geothermal potential. The mine water contained high concentrations of chloride (59.6 g/L), Na (28 g/L), K (1.75 g/L), Ca (7.2 g/L), Mg (0.63 g/L), and Li (66 mg/L), especially in water from the old dewatering system. Metal concentrations were especially elevated in the old mine shafts, with high amounts of Fe (1990 mg/L), Mn (600 mg/L), Zn (460 mg/L), Pb (4 mg/L), and Ni (11.4 mg/L). The Cl/Br molar ratios of the water was high, which may indicate the possible leaching of natural halite from the evaporite deposits in the aquifer recharge area. The mine water had the most elevated temperatures and are, possibly, representative of the extent of equilibration in most of the reservoir. The estimated mean temperatures in the geothermal reservoir, based on the triangular (Giggenbach) Na-K-Mg diagram, was 190ºC for equilibrated waters, which may justify the development of this geothermal resource. The geothermal characteristics imply convection of groundwater to 2500-3000 m below sea level, in agreement with the hydrodynamic model proposed.
Consideration is given to the possibility of ocean thermal energy conversion (OTEC) by the deliberate salinization of surface seawater. The proposed technique is similar to traditional OTEC, with one important exception: rather than cold water being brought from the bottom to the surface, the warm surface water is circulated to the bottom, cooled there, and lifted back to the surface. The entire process is driven by the induced salinity gradient at the surface. As a result, there is no need for a pumping system to bring the cold bottom water to the surface. Two methods are explored for surface salinity enhancement, namely solar evaporation and the direct addition of salt to the seawater.
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Busqué , R.; Torres, R.; Grau, J.; Roda, V.; Husar, A. International journal of hydrogen energy Vol. 42, num. 30, p. 19114-19125 DOI: 10.1016/j.ijhydene.2017.06.125 Data de publicació: 2017-07-27 Article en revista
A two-dimensional axisymmetric model is developed to study the hydrogen absorption reaction and resultant mass and heat transport phenomena inside a metal hydride canister. The model is compared against published literature and experimental data. Experimental tests are performed on an in-house fabricated setup using different cooling scenarios. An extensive study on the effects of the metal properties on charging performance is carried out through non-destructive testing (NDT). Results show that the properties that most influence the charging performance are: absorption rate constant (Ca), activation energy (Ea) and thermal conductivity (km). A Higher porosity (e) reduces charging time and amount of hydrogen stored while a higher cooling level produces a faster charging process. These results can be used to select metal hydride materials but also to estimate the metal hydride internal state and the process can be used for future evaluation of metal hydride degradation.
Castilla, R.; Gamez-Montero, P.J.; Raush, G.; Codina-Macia, Esteban Journal of fluids engineering. Transactions of ASME Vol. 139, num. 11, p. 1-9 DOI: 10.1115/1.4037060 Data de publicació: 2017-07-21 Article en revista
A new approach based on the open source tool OpenFOAM is presented for the numerical simulation of a mini gerotor pump working at low pressure. The work is principally focused on the estimation of leakage flow in the clearance disk between pump case and gears. Two main contributions are presented for the performance of the numerical simulation. On one hand, a contact point viscosity model is used for the simulation of solid–solid contact between gears in order to avoid the teeth tip leakage. On the other hand, a new boundary condition has been implemented for the gear mesh points motion in order to keep the mesh quality while moving gears with relative velocity. Arbitrary coupled mesh interface (ACMI) has been used both in the interface between clearance disk in inlet/outlet ports and between clearance disk and interteeth fluid domain. Although the main goal of the work is the development of the numerical method rather than the study of the physical analysis of the pump, results have been compared with experimental measurement and a good agreement in volumetric efficiency and pressure fluctuations has been found. Finally, the leakage flow in the clearance disk has been analyzed.