Persona: Ibarra Mollá, Mercedes
Cargando...
Dirección de correo electrónico
mibarra@ind.uned.es
ORCID
Fecha de nacimiento
Proyectos de investigación
Unidades organizativas
Puesto de trabajo
Apellidos
Ibarra Mollá
Nombre de pila
Mercedes
Nombre
17 resultados
Resultados de la búsqueda
Mostrando 1 - 10 de 17
Publicación Advances in aerosol optical depth evaluation from broadband direct normal irradiance measurements(Elsevier, 2021-06) Salmon, Aloïs; Quiñones, Gonzalo; Soto, Gonzalo; Polo, Jesús; Gueymard, Christian; Ibarra Mollá, Mercedes; Escobar, Rodrigo; Marzo, AitorAerosols are part of the attenuation processes that impact solar radiation within the atmosphere. They influence the availability and spectrum of the solar resource for each location at the earth’s surface. The present study presents advances in the development of a methodology intended to estimate the aerosol optical depth (AOD) at a given location from broadband direct normal irradiance (DNI) measurements and an appropriate radiative transfer model (RTM) operated backwards. For this purpose, databases provided by AERONET and BSRN at 16 stations throughout the world are jointly employed as inputs to the proposed methodology. The validation of two RTMs (SMARTS and SOLIS) is first undertaken to estimate DNI under clear-sky conditions at each station, assuming both AOD and additional atmospheric inputs are known from sunphotometric measurements. Results indicate that both models achieve good performance, characterized by a relative rRMSE of 3.2% for SMARTS and 3.8% for SOLIS. In the second, and most important stage, the AOD at 550 nm (AOD550) is derived using these models again, but in an iterative mode, now using the 1-minute DNI measurements as inputs. Periods of clear line of sight to the sun first need to be selected from the irradiance measurement record. This, along with other difficulties, make this operation prone to errors when only DNI measurements are available. In spite of this, the results show that AOD can be estimated with a 16-site average mean bias error of only between −0.024 and 0.015 AOD unit and an absolute RMSE between 0.025 and 0.050 AOD unit (compared to the AERONET ground truth), depending on model. Notable improvements are obtained if secondary atmospheric variables are extracted from the MERRA-2 reanalysis and are included as inputs for local computations. The present results suggest that the method is able to compare favorably with AOD estimates from MERRA-2 predictions or MODIS observations, for instance.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-César; Zaragoza, Guillermo; Blanco Galvez, Julian; 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 Integration enhancements of a solar parabolic trough system in a Chilean juice industry: Methodology and case study(Elsevier, 2021-08) Crespo, Alicia; Muñoz, Iván; Platzer, Werner; Ibarra Mollá, MercedesA Chilean company dedicated to grape juice production used a 696 m2 parabolic trough collector to pre-heat the feed water of a liquefied petroleum gas boiler in a temperature range of 20–90 °C. During 2017 the solar field generated 241 MWhth of heat, a low value for a concentration collector of such dimensions located in a place with high irradiation. This study presents a methodology to identify enhanced scenarios of solar heat integration into a grape juice industry and among them select the best scenario from an energetic perspective. This methodology started with data gathering of the thermal processes of the industry and the solar field (monitoring campaign and logbook of the industry) to generate the annual thermal demand. In a second step, the maximum theoretical generation potential of the solar field (1,107 MWhth) was obtained with simulations in TRNSYS 18. Then, a Pinch Analysis to the process streams was performed to confirm that a higher solar heat integration potential (520 MWhth) existed. The next step consisted of identifying different scenarios to increase the solar heat integration and analyzing them with simulations in TRNSYS 18 to identify the best-case scenario. The main increase on the solar fraction was achieved for the scenario when the collector working temperature was increased up to 140 °C and when heat was integrated at process level. Furthermore, it was concluded that one of the reasons for low solar fraction was the low thermal demand during months with high solar irradiation.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 Experimental analysis of an air gap membrane distillation solar desalination pilot system(Elsevier, 2011-09) Guillén-Burrieza, Elena; Blanco Galvez, Julian; Zaragoza, Guillermo; Alarcón-Padilla, 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 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 Galvez, Julian; 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 Comparative evaluation of two membrane distillation modules(Elsevier, 2011-07) Guillén-Burrieza, Elena; Blanco Galvez, Julian; Alarcón-Padilla, Diego-César; 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.Publicación Theoretical technical–economic comparison of hybrid energy for gas and solar concentration plants in the Region of Antofagasta Chile(Elsevier, 2023-02) Hernández Moris, Catalina; Felbol, Carlos; Cerda, Maria Teresa; Ibarra Mollá, MercedesElectricity demand from mining industry in Chile will increase up to 34 % in the next 10 years. The Antofagasta region has several mining operations and gas pipelines, in addition to being an area with very high solar resource availability. This study focuses on reviewing hybridization alternatives for combined cycle plants with concentrating solar generation technologies. In this work a techno-economic analysis of two alternative small scale hybridized solar-combined cycle technologies is developed, a solarized combined cycle with STP and a solarized combined cycle with PTC. To perform the solar concentration systems simulations, TRNSYS software was used for PTC, and Solstice software for STP system, while the thermodynamic simulation for the combined cycle system was developed using EES software. The LCOE was calculated for all plants considering a fuel cost of 66 USD/MWh. LCOE obtained for combined cycle is 202 USD/MWh, while LCOE for combined cycle with STP integration is 149 USD/MWh, and LCOE for combined cycle with PTC integration is 197 USD/MWh. The lowest LCOE is achieved with the STP integration, since part of the fuel that feeds the combined cycle is replaced by solar energy, avoiding the emission of 16,603 tons of CO2.Publicación Performance of an Organic Rankine Cycle with two expanders at off-design operation(Elsevier, 2019-02-19) Ibarra Mollá, Mercedes; Rovira de Antonio, Antonio José; Alarcón-Padilla, Diego-CésarThe objective of this work was to simulate the behavior of an Organic Rankine Cycle (ORC) system with two expanders in series at off-design working conditions. The influence of both the intermediate pressure and the volumetric expansion ratio of the expanders on the off-design performance of the ORC was studied and the irreversibilities of the components were analyzed. The performance of the ORC with two expanders for two different designs was also discussed. The thermal efficiency reached using two expanders was higher than the obtained using only one. However, this increase conveyed an increase in the complexity of the design and control of the expanders. As an additional conclusion, it was found that the influence of the intermediate pressure is higher than that of the volume expansion ratio of each expander. The irreversibility of the first expander was mainly due to leaks. However, the performance of the second expander was particularly affected by the difference between the discharged pressure and the condensation pressure. The off-design analysis allowed the definition of a methodology to achieve the desired power with the maximum thermal efficiency, and the identification of the best actuation for the part load operation.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-Padilla, Diego-César; Zaragoza, Guillermo; Blanco Galvez, Julian; 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.