Persona: Ibarra Mollá, Mercedes
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Publicación Evaluación tecno-económica de sistemas basados en ciclos Rankine orgánicos de pequeña potencia para su integración en sistemas termosolares(Universidad Nacional de Educación a Distancia (España). Escuela Técnica Superior de Ingenieros Industriales. Departamento de Ingeniería Energética, 2016-06-22) Ibarra Mollá, Mercedes; Rovira de Antonio, Antonio; Alarcón Padilla, Diego-CésarEl objetivo de este trabajo era el estudio tecnoeconómico de una planta de ciclo Rankine orgánico (CRO) de baja potencia (<10 kWe) que funcionara con energía solar de media temperatura (100-250ºC). Uno de los primeros objetivos era desarrollar una metodología de diseño del sistema, tanto del sistema solar como del sistema CRO. Para ello se ha presentado, un modelo para la simulación anual de un campo solar y la experimentación realizada con el captador NEPSolar Polytrough 1200, que permitió obtener Ja curva de rendimiento de dicho captador. Por otro lado, en esta tesis se ha desarrollado el modelo de simulación de CRO, que permite el análisis de varios diseños, fluidos (SES36 y R245fa) y condiciones de trabajo. Una instalación experimental permitió la validación del modelo, corroborando su capacidad de previsión de cálculo de la potencia producida. Este modelo de simulación de CRO ha permitido analizar detalladamente el comportamiento de los CRO a cargas parciales, tanto con un expansor, como con dos expansores, en ros que se estudió el comportamiento de los ciclos a diferentes condiciones de trabajo. Los resultados de este análisis han permitido proponer una metodología para seleccionar el punto de operación de los ciclos más adecuado para cada potencia demandada. En el diseño del sistema, el primer problema a resolver en ros CRO con dos expansores en serie ha sido la selección de los parámetros de diseño que optimizara el comportamiento del ciclo a cargas parciales. En particular, la elección de la presión intermedia entre expansores adecuada era fundamental para el buen funcionamiento del ciclo posterior. Para ello se analizaron diferentes metodologías, siendo la que tenía mejores resultados la estrategia de elegir el conjunto de valores que hace que los rendimientos de los expansores sean similares. Los modelos CRO desarrollados en esta tesis han permitido la generación de los mapas de operación, que a su vez han permitido determinar la operación del sistema a cargas parciales con menores tiempos de computación. Utilizando estos mapas se ha realizado la simulación anual del comportamiento de un sistema CRO acoplado un campo solar. Se han analizado cuatro sistemas, combinando CRO de uno y dos expansores y captadores cilindroparabólicos de pequeña apertura y captadores planos de ultra-vacío. Por último, se ha realizado un análisis económico, en el que se incluye un cálculo determinístico del LCOE, la optimización del par múltiplo solar-almacenamiento térmico (minimizando el coste nivelado de la energía), un análisis de sensibilidad de los costes y un análisis estadístico de los resultados. Por tanto, el trabajo desarrollado en la tesis ha permitido identificar una ventana de diseño en cuanto a posibles captadores solares, fluidos de CRO, condiciones de trabajo y máquinas de expansión, considerando siempre la operación real y el comportamiento real de ras máquinas y equipos involucrados, tanto del ciclo Rankine orgánico como del sistema solar y pudiendo determinar las ventajas y desventajas de cada diseño.Publicación Proposal of a microchannel receiver for Fresnel technology to supply solar heat for industrial processes(Elsevier, 2023-09-30) Stojceska, V.; Reay, David A.; Montes Pita, María José; Ibarra Mollá, MercedesThis work is focused on the linear Fresnel technology to supply solar heat for industrial processes, proposing a new microchannel receiver design for pressurised gases. This design consists of two absorber panels converging at the focal line of the Fresnel system; each of these panels consists of a compact core fin structure attached to both front and back plates. The fluid flows through the receiver along its length in several passes, so that the compactness is constant and greater than in the previous pass. This arrangement improves heat transfer and, therefore, the cooling of the more thermally stressed areas of the panel, without over penalising the pressure drop. A thermal resistance model has been formulated to quantify the fluid heating along the panel length and the thermal gradient along the panel thickness. This model has been used to perform a thermo-exergy optimisation based on several characteristic parameters: the aperture half-angle of the cavity shaped by the two converging panels; and the channels dimensions in each pass of the panel. For each of these parameters, a maximum exergy efficiency has been obtained accounting for the receiver heat losses, the fluid pressure drop and the optical performance of the primary mirror field.Publicación Experimental analysis of an air gap membrane distillation solar desalination pilot system(Elsevier, 2011-09) Guillén Burrieza, Elena; Blanco, Julián; Zaragoza, Guillermo; Alarcón, Diego-César; Palenzuela, Patricia; Ibarra Mollá, Mercedes; Gernjak, Wolfgang; https://orcid.org/0000-0003-4145-9224; https://orcid.org/0000-0001-7329-380X; https://orcid.org/0000-0002-4452-9980; https://orcid.org/0000-0002-8843-8511; https://orcid.org/0000-0001-8044-969X; https://orcid.org/0000-0001-9859-2435; https://orcid.org/0000-0003-3317-7710Freshwater shortage difficulties make it necessary to find new sources of supply. Nowadays desalination is the solution adopted in many countries to solve this problem. All around the planet, regions with lack of freshwater match up with those with large amounts of available solar radiation. Therefore, solar desalination can be a suitable and sustainable option to tackle the water scarcity problems in those particular areas, especially in the coastal ones where the majority of human population lives. Membrane distillation (MD) is a thermal membrane technology developed since late 60´s which uses low exergy heat to drive a separation process in aqueous solutions. One of its applications is desalination where thanks to its separation principle, very high distillate quality can be obtained. Amongst its advantages, its low operating temperatures, ranging between 60-90º C [Lawson and Lloyd, 1997] make possible the use of low-grade heat, the kind of energy easily delivered by static solar collectors, as the only thermal supply. This, jointly with its low operational pressure and small footprint, make MD coupled with solar energy (Solar Membrane Distillation) in principle, a promising technology. Under the framework of a European project (MEDESOL Project) funded by the European commission, an innovative desalination system based on solar air gap membrane distillation has been investigated. The system is intended to be technically simple to operate, robust and able to cover water demands of small settlements. The experimental set-up was built at Plataforma Solar de Almería facilities (leading partner) and tested during 4 months. The desalination system consists of a three MD desalination modules system supplied with the thermal energy of a static collector’s solar field. Desalination and solar circuits are connected through a plate heat exchanger especially coated to withstand hot seawater operational conditions. The system was run during solar hours (as the layout doesn’t contemplate heat storage) and the experiments were designed to characterize the system. The overall performance of the system was evaluated with both tap water and a 35 g L-1 NaCl aqueous solution. The distillate production and quality were evaluated as a function of the operational parameters, as well as the thermal consumption and specific desalination parameters such as performance ratio (PR). The system can work at temperatures up to 95ºC on the hot feed side and up to 60 ºC on the refrigeration side. This paper will show the experimental results as well as the operational experiences of the system.Publicación Assessment of different configurations for combined parabolic-trough (PT) solar power and desalination plants in arid regions(Elsevier, 2011-08) Palenzuela, Patricia; Zaragoza, Guillermo; Alarcón-Padilla, Diego C; Blanco, Julián; Guillén, Elena; Ibarra Mollá, Mercedes; https://orcid.org/0000-0001-8044-969X; https://orcid.org/0000-0002-8843-8511; https://orcid.org/0000-0002-4452-9980; https://orcid.org/0000-0001-7329-380X; https://orcid.org/0000-0003-4145-9224The combination of desalination technology into concentrating solar power (CSP) plants needs to be considered for the planned installation of CSP plants in arid regions. There are interesting synergies between the two technologies, like the possibility of substituting the condenser of the power cycle for a thermal desalination unit. This paper presents a thermodynamic evaluation of different configurations for coupling parabolic-trough (PT) solar power plants and desalination facilities in a dry location representing the Middle East and North Africa (MENA) region. The integration of a low-temperature multi-effect distillation (LT-MED) plant fed by the steam at the outlet of the turbine replacing the condenser of the power cycle has been simulated and compared with the combination of CSP with a reverse osmosis (RO) plant. Furthermore, an additional novel concept of concentrating solar power and desalination (CSP+D) has been evaluated: a LT-MED powered by the steam obtained from a thermal vapour compressor (TVC) using the exhaust steam of the CSP plant as entrained vapour and steam extracted from the turbine as the motive vapour of the ejector. This new concept (LT-MED-TVC) has been analyzed and compared with the others, evaluating its optimization for the integration into a CSP plant by considering different extractions of the turbine.Publicación Modeling of the heat transfer of a solar multi-effect distillation plant at the Plataforma Solar de Almería(Elsevier, 2011-07) Palenzuela, Patricia; Alarcón, Diego; Blanco, Julián; Guillén, Elena; Ibarra Mollá, Mercedes; Zaragoza, Guillermo; https://orcid.org/0000-0001-8044-969X; https://orcid.org/0000-0002-8843-8511; https://orcid.org/0000-0001-7329-380X; https://orcid.org/0000-0003-4145-9224; https://orcid.org/0000-0002-4452-9980Potable water supply by desalination systems has a significant role in today’s developing world. Multi-effect distillation (MED) is a progressing, low cost and easy operating system to produce drinking and pure water for both social and industrial applications. It is very important to understand in detail the process elements in order to determine the effects of the important design and operating variables on the parameters controlling the performance of the plant. A model is developed for the MED plant located at the Plataforma Solar de Almería (PSA), in the southeast of Spain. It is a vertical-arrangement forward-feed MED plant with pre-heaters, which uses hot water as the thermal energy source. The model has been developed dividing the MED plant into four blocks: the heater (consisting of the first effect), the evaporators (consisting of effects 2 to N), the pre-heaters (for effects 1 to N – 1) and the condenser (after effect N). To solve the model, a parameterization of the overall heat transfer coefficient of the four blocks has been carried out with experimental data for a wide range of operation, based on correlations found by other authors for similar plants. The adjustments were good for all the components with the exception of the condenser, which seems to behave differently than in other cases reported in the literature.Publicación Performance of a 5kWe Organic Rankine Cycle at part-load operation(Elsevier, 2014-05) Ibarra Mollá, Mercedes; Rovira de Antonio, Antonio José; Alarcón Padilla, Diego César; Blanco, Julián; https://orcid.org/0000-0002-8843-8511; https://orcid.org/0000-0001-7329-380XThis paper analyzes the performance of an Organic Rankine Cycle (ORC) system at part load operation. The objective is to understand its behavior from a thermodynamic perspective, identifying which elements are the most critical and which are the best operating points for each level of demanded power. This paper also compares two working fluids: R245fa and Solkatherm ES36 (SES36) for the same cycle specifications. The results have shown that the scroll isentropic efficiency has a great influence on the cycle performance and its thermal efficiency and that SES36 arises as a potential better fluid than R245fa. At the given maximum and minimum temperatures, the best operation point was determined. This allows reaching a maximum efficiency for each demanded level of power; depending on the required amount of power, the expander speed and the working pressure are adjusted.Publicación Latent thermal energy storage for solar process heat applications at medium-high temperatures – A review(Elsevier, 2019-11) Crespo, Alicia; Barreneche, Camila; Ibarra Mollá, Mercedes; Platzer, Werner; https://orcid.org/0000-0003-4616-0221; https://orcid.org/0000-0003-3636-3180Solar thermal energy has the potential to cover the heat demands of industrial processes. However, there may be a time mismatch between energy supplied by the solar field and the process demand. In this case, a thermal energy storage (TES) allows the use of heat at hours without solar irradiation available. Thermal energy storage (TES) for solar hot water or heating systems using low temperatures have been optimized since many decades and are in a mature stage. Developments at high temperatures (above 200 °C) for CSP applications have also been deeply studied. However, until this present paper, limited attention has been paid to TES for solar thermal industrial applications at medium-high temperatures (120 - 400°C), where there is a potentially huge demand. When discussing TES several aspects have to be discussed: the energy demand that TES is going to be designed to supply, the material where the energy will be stored and the performance of the TES system which includes not only the material but also tanks, piping and connections. In this review, food, brewery and chemical industries were identified as the industries with higher potential in which TES and solar energy could be integrated. Heat integration methodologies have been reviewed to optimize the use of the solar energy by the industrial processes. Regarding the material, latent heat storage or phase change materials (PCM) were selected because they are a very promising type of storage to be integrated in thermal industrial processes, although the state of the art of latent heat thermal storage (LHTES) systems is still far from broad commercialization. Until now, no reviews of latent heat storage for industrial applications at medium-high temperatures (120 - 400 °C) have been published. Therefore, literature related to PCM and LHS systems using PCM materials to be used in industrial thermal processes is here reviewed in order to have a general overview of the available technologies for their integration together with solar thermal energy in industrial processes at both experimental and numerical level. More than 100 potential PCMs for heat storage applications in the range of temperatures 120 - 400 °C have been found. Inorganic eutectic compositions are the group with more potentially available PCM for these applications, with values of heat of fusion between 74 and 535 kJ/kg. Finally, the works related to the performance of the system from the experimental and modelling point of view were presented. The review of experimental TES systems which include PCM in the studied range of temperatures 120 - 400 °C showed that most of the experimental set-ups were developed for direct steam generation for CSP applications. Regarding numerical modelling, the type of configuration more simulated is the shell and tube configuration.Publicación Parametric equations for the variables of a steady-state model of a multi-effect desalination plant(Taylor and Francis Group, 2012-07-10) Palenzuela, Patricia; Alarcón, Diego; Zaragoza, Guillermo; Blanco, Julián; Ibarra Mollá, MercedesIn the present work a steady-state model is developed of an MED plant. Its development and validation have been carried out by experimental data obtained from an MED pilot plant located at the Plataforma Solar de Almería (PSA), in the southeast of Spain. It is a vertical-arrangement forward-feed MED plant with pre-heaters, which uses hot water as the thermal energy source. In order to run the model a series of parametric equations for these variables: the overall heat transfer coefficient for the first effect (Uh), the overall heat transfer coefficient for the pre-heaters (Up(i)), the vapor temperature inside the first effect, (Tv(1)) and the cooling seawater outlet temperature (Tcwout) have been determined. They have been obtained from a three-level factorial experimental design (3k), performing a total of 81 experiments (34). The results obtained showed a good fit to the estimated models for the response variables.Publicación Performance of a 5 kWe solar-only organic Rankine unit coupled to a reverse osmosis plant(Elsevier, 2014) Ibarra Mollá, Mercedes; Rovira de Antonio, Antonio José; Alarcón Padilla, Diego C.; Zaragoza, Guillermo; Blanco Gálvez, Julián; https://orcid.org/0000-0002-8843-8511; https://orcid.org/0000-0002-4452-9980; https://orcid.org/0000-0001-7329-380XOrganic Rankine Cycle (ORC) systems are one of the most promising energy conversion technologies available for remote areas and low temperature energy sources. An ORC system works like a conventional Rankine cycle but it uses an organic compound as working fluid, instead of water. A small ORC unit coupled with a solar thermal energy system could be used to convert solar thermal energy into electricity in remote areas, offering an alternative to Photovoltaic (PV) systems to provide the energy required by desalination applications like reverse osmosis (RO). In this work an analysis of the performance of a specific solar desalination ORC system at part load operation is presented, in order to understand its behavior from a thermodynamic perspective and be able to predict the total water production with changing operation conditions. The results showed that water production is around 1.2 m3/h, and it is stable during day and night thanks to the thermal storage and only under bad irradiance circumstances the production would stop.Publicación Comparative evaluation of two membrane distillation modules(Elsevier, 2011-07) Guillen Burrieza, Elena; Blanco Gálvez, Julián; Alarcón Padilla, Diego C.; Zaragoza, Guillermo; Palenzuela, Patricia; Ibarra Mollá, Mercedes; https://orcid.org/0000-0003-4145-9224; https://orcid.org/0000-0001-7329-380X; https://orcid.org/0000-0002-8843-8511; https://orcid.org/0000-0002-4452-9980; https://orcid.org/0000-0001-8044-969XFreshwater shortage difficulties make it necessary to find new sources of supply. Nowadays desalination is the solution adopted in many countries to solve this problem. All around the planet, regions with lack of freshwater match up with those with large amounts of available solar radiation. Therefore, solar desalination can be a suitable and sustainable option to tackle the water scarcity problems in those particular areas, especially in the coastal ones. Membrane distillation (MD) is a thermal membrane technology developed since late 60’s which uses low exergy heat to drive a separation process in aqueous solutions. One of its applications is desalination where thanks to its separation principle, very high distillate quality can be obtained. MD is a thermally driven process that differs from other membrane technologies in that its driving force, rather than the total pressure, is the difference in water vapour pressure across the membrane, caused in turn by a temperature difference between the cold and the hot side of it. In comparison with other membrane-based desalination processes like reverse osmosis (RO), MD shows very high rejection rates and much lower operational pressures, also the nature of MD membranes (larger pore sizes than RO) makes them much less sensitive to fouling. Compared to conventional thermal desalination processes like MSF or MED, MD is less demanding regarding vapor space and building material’s quality [1] leading to potential lower construction costs. Amongst its advantages, its low operating temperatures (ranging between 60–90°C [2]) make possible the use of low-grade heat, the kind of energy delivered by static solar collectors, as the only thermal supply. This, jointly with its low operational pressure and small footprint, make solar membrane distillation (SMD) in principle, a promising technology. Despite these advantages, SMD has been developed to a lesser extent, compared with other solar desalination technologies like PV-driven RO or solar stills, and although many encouraging laboratory experiences can be found in literature, large-scaling and module design is still an issue. It is precisely because of this preliminary state MD is in, that very preliminary, low energy efficiency and not commercial available MD prototypes are still found. In MD there is still a trade-off between efficiency (heat consumption) and production (distillate per square meter of membrane), as a result very high specific distillate fluxes can be attained (up to 80 kg h–1 m–2 of membrane [3]) but heat losses (mainly trough the membrane by conduction) are still substantial. Under the framework of an European project (MEDESOL: Seawater Desalination by Innovative Solar Powered Membrane Distillation) which main objective was to develop a stand-alone desalination system based on multi stage MD to supply decentralized rural areas [4], the status and future possibilities of currently developed MD have been evaluated. This paper presents the results obtained from the experiments realized with two different pre-commercial MD modules, coupled to a solar field comprised of static collectors. Both modules were tested in the same facility under the same conditions, in order to make a reliable comparison between them. Data on energy efficiency, production ratios and operational issues will be shown.