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K.s. Rajan - One of the best experts on this subject based on the ideXlab platform.

  • Lowered total solidification time and increased discharge rate of reduced graphene oxide-Solar Salt composites: Potential for deployment in latent heat thermal energy storage system
    Solar Energy, 2020
    Co-Authors: M.k. Saranprabhu, D. Chandini, P. Bharathidasan, S. Devaraj, K.s. Rajan
    Abstract:

    Abstract Solar Salt is a useful energy storage medium and a heat transfer fluid for concentrated Solar thermal applications. The present work explores the use of reduced graphene oxide (rGO) nanostructures as an additive to Solar Salt, to improve its thermophysical properties. Reduced graphene oxide nanostructures at weight fractions of 0.125 wt% and 0.5 wt% were added to the Solar Salt, leading to rGO-Solar Salt composites. The thermophysical characterization experiments revealed that the specific heat in the 0.5 wt% rGO-Solar Salt nanocomposite was elevated by 6% over the temperature range of 50–270 °C. The time required for complete solidification of 0.125 wt% and 0.5 wt% was reduced by 43% and 49%. In the discharge cycle, the heat transfer rate was amplified by 90% and 138% respectively for 0.125 wt% and 0.5 wt% rGO-Solar Salt nanocomposites, attributable to thermal conductivity enhancement, specific heat augmentation and heterogeneous nucleation. Thus, rGO-Solar Salt composites are suitable for use as latent heat thermal energy storage medium in Solar thermal applications.

  • Enhancement of solid-phase thermal conductivity and specific heat of Solar Salt through addition of MWCNT: new observations and implications for thermal energy storage
    Applied Nanoscience, 2019
    Co-Authors: M.k. Saranprabhu, K.s. Rajan
    Abstract:

    Solid-phase thermophysical properties of Solar Salt (a mixture of NaNO3 and KNO3) influence the performance of sensible heat and latent heat thermal energy storage systems. Solar Salt’s lower thermal conductivity imparts kinetic limitation during the discharge cycle and hence its thermal conductivity needs to be enhanced. This work is aimed at studying the influence of MWCNT incorporation on the improvement of solid-phase thermophysical properties of Solar Salt. Accordingly, experiments were carried out to study the influence of method of MWCNT-Solar Salt preparation, MWCNT concentration and temperature on solid-phase specific heat and thermal conductivity. Our results reveal that 0.5 wt% MWCNT-Solar Salt composite prepared by ultrasonication and milling for an appropriate time lead to 18.3% enhancement in the solid-phase thermal conductivity and 18% enhancement in the solid-phase specific heat. In addition, the total energy storage capacity over the temperature range of 50–270 °C (including solid–liquid phase change) is amplified by 11.5%. These results augur well for deployment of the MWCNT-Solar Salt composite in the thermal energy storage system as a storage medium.

  • Magnesium oxide nanoparticles dispersed Solar Salt with improved solid phase thermal conductivity and specific heat for latent heat thermal energy storage
    Renewable Energy, 2019
    Co-Authors: M.k. Saranprabhu, K.s. Rajan
    Abstract:

    Abstract Composites comprising MgO nanoparticles as the dispersed phase and solid phase Solar Salt as the matrix have been prepared through solid-state mixing. The inclusion of MgO nanoparticles had very little influence on the solid-liquid phase change temperature and the latent heat of Solar Salt. However, the solid phase thermal conductivity of MgO-Solar Salt was elevated by 17.5% with the dispersion of 0.25 wt% MgO nanoparticles. The clustered nature of MgO nanoparticles and their presence at the interface between Solar Salt particles with reduced resistance might have contributed to the solid phase thermal conductivity enhancement for this composition of the composite. The maximum enhancement in specific heat of MgO-Solar Salt composite (14%) was observed at another composition (1 wt%), revealing the requirement of different composition for optimum thermal conductivity and optimum specific heat. The solidification time for 0.25 wt% composite was 30% lower than that of the Solar Salt. Also, the rate of discharge from 0.25 wt% composite was 42.4% higher than that of Solar Salt. The corresponding data for the composite containing 2 wt% MgO are 13.8% and 33.8% respectively. These composites can be used in latent heat thermal energy storage systems.

Thomas Bauer - One of the best experts on this subject based on the ideXlab platform.

  • Thermal stability of Solar Salt at 650 °C - A deep dive into molten nitrate Salt chemistry
    2020
    Co-Authors: Alexander Bonk, Markus Braun, Andrea Hanke, Veronika Anna Sötz, Thomas Bauer
    Abstract:

    At the last SolarPaces conference we demonstrated that the thermal stability of conventional Solar Salt (60-40wt % NaNO3-KNO3) is substantially increased when the storage system including the gas system is sealed.[4] The operating temperature could therefore successfully be enhanced to 600 °C. During the last months we have investigated the temperature regime above 600 °C to push the thermal stability limit even further, e.g. up to 650 °C. In closed systems all gas species relevant for regeneration of the Salt (mainly O2 and NOx), will accumulate in the gas phase and shift chemical equilibria to the nitrate and nitrite side of Eq (1) and (2) (shown later), respectively. Yet, it remains unclear which ions participate in the decomposition process into oxide ions. In this study we explored the role of the nitrate and nitrite ions in the decomposition reactions at temperatures up to 650 °C to confirm their role in the overall decomposition process and the importance of gas composition.

  • Enhancing the Thermal Stability of Solar Salt up to 600°C in Extended Lab-Scale Experiments
    SOLARPACES 2019: International Conference on Concentrating Solar Power and Chemical Energy Systems, 2020
    Co-Authors: Alexander Bonk, Markus Braun, Andrea Hanke, Veronika Anna Sötz, Thomas Bauer
    Abstract:

    Future trends push TES towards higher temperatures to increase Solar-to-electricity conversion efficiency and novel storage materials are often considered the only viable option. To date these candidates suffer from either high costs (carbonate Salts containing Li+) or severely attack structural materials (chloride Salts) and are far from industrial implementation. An alternative approach is investigated in our work - the use of the classical Solar Salt with sophisticated gas management which selectively shifts the chemical equilibrium to the stable nitrate-side of the decomposition reaction. We demonstrate that the thermal stability of conventional Solar Salt (60-40wt % NaNO3-KNO3) is substantially increased when the storage system including the gas system is simply but effectively sealed. The key to this novel data is the unique feature of in-situ sample extraction and post-analysis that allows for a quasi in-situ determination of molten Salt stability in terms of nitrite and oxide ion formation. Our investigations present clear evidence on the enhanced thermal stability at an experimental scale of about 100 g that is two magnitudes larger than conventional thermal analysis experiments.

  • With a view to elevated operating temperatures in thermal energy storage - Reaction chemistry of Solar Salt up to 630°C
    Solar Energy Materials and Solar Cells, 2020
    Co-Authors: Veronika Anna Sötz, Alexander Bonk, Thomas Bauer
    Abstract:

    Abstract Sensible heat storage is a cost-efficient and scalable technology for energy storage. The state-of-the-art storage systems in concentrating Solar power (CSP) plants use the storage material Solar Salt, which is a nitrate Salt mixture. Chemical stability of this Salt material is crucial for lifetime reliance, and for development of the storage technology towards higher temperatures. High temperatures enhance the storage capacity, but also promote decomposition reactions. For instance, harmful gases can evolve, and oxide ions are produced, which aggravate corrosion. Up to now, it is unclear how to describe the Salt chemistry, and how to quantitatively predict the problematic decomposition products. The experimental method in this study is chosen with regard to the exclusion of mass transport limitations. Thin films of Salt are heated to 560–630 °C. The Salt composition is analyzed by ion chromatography and acid-base titration. The ratio of nitrite to nitrate ions stabilizes, which indicates chemical equilibrium of the nitrite forming reaction. The oxide content increases continuously over time, and is interpreted in terms of a kinetic rate law. A consistent mathematical description of Solar Salt chemistry at high temperatures (≥560 °C) in contact with air is presented. It includes thermodynamic parameters, in particular the reaction enthalpy of 95 ± 4 kJ⋅mol−1 and entropy of 86 ± 5 J⋅mol−1⋅K−1 for the nitrate-nitrite reaction. The microkinetics of the oxide ion formation are characterized by an activation energy of 42 ± 3 kJ⋅mol−1. The work presented finally contributes to a forecast of material stability at and above 560 °C.

  • Solar Salt – Pushing an old material for energy storage to a new limit
    Applied Energy, 2020
    Co-Authors: Alexander Bonk, Markus Braun, Veronika Anna Sötz, Thomas Bauer
    Abstract:

    Abstract The implementation of inexpensive and reliable energy storage technologies is crucial for the decarbonisation of energy intensive industry branches and energy supply. Sensible thermal energy storage (TES) in molten Salts is a key technology for storage of heat in the scale of gigawatt hours but currently limited to operating temperatures of 560 °C. Increasing the maximum operating temperature while maintaining thermal stability of the storage medium is one of the main challenges next-Generation TES systems are facing. Extending the upper temperature limit by only 40 °C increases the storage capacity by more than 16% allowing for more compact storage designs and cost savings in the $ million-range for large scale storage units. Here we propose a novel storage technology from a materials point of view that pushes the thermal stability limit of Solar Salt up to 600 °C by simply but effectively sealing the storage unit including the gas system. The concentration of the unstable nitrite ion and of the corrosive oxide ion could be reduced by 16% and 75%, respectively at 600 °C, compared to a Salt system with open atmosphere. We present clear evidence of the enhanced thermal stability in long-term, 100 g-scale test campaigns at previously unequalled temperatures. These findings constitute a major advance in the design and engineering of next generation storage systems.

  • Enhancing the thermal stability of Solar Salt to and above 600°C in extended lab-scale
    2019
    Co-Authors: Alexander Bonk, Markus Braun, Veronika Anna Sötz, Thomas Bauer
    Abstract:

    Future trends push TES towards higher temperatures to increase Solar-to-electricity conversion efficiency and novel storage materials are often considered the only viable option. To date these candidates suffer from either high costs (carbonate Salts containing Li+) or severely attack structural materials (chloride Salts) and are far from industrial implementation. An alternative approach is investigated in our work, the use of the classical Solar Salt with sophisticated gas management which selectively shifts the chemical equilibrium to the stable nitrate-side of the decomposition reaction. We demonstrate that the thermal stability of conventional Solar Salt (60-40wt % NaNO3-KNO3) is substantially increased when the storage system including the gas system is simply but effectively sealed. The key to this novel data is the unique feature of in-situ sample extraction and post-analysis that allows for a quasi in-situ determination of molten Salt stability in terms of nitrite and oxide ion formation. Our investigations present clear evidence on the enhanced thermal stability and at a scale of experiments that is two magnitudes larger than in conventional experiments.

Yulong Ding - One of the best experts on this subject based on the ideXlab platform.

  • Effect of SiO2 nanoparticle addition on the wetting and rheological properties of Solar Salt
    Solar Energy Materials and Solar Cells, 2020
    Co-Authors: Argyrios Anagnostopoulos, Anabel Palacios, M.h. Navarro, Sonia Fereres, Yulong Ding
    Abstract:

    Abstract Molten Salt based nanofluids are involved in Thermal Energy Storage (TES) Systems, both as heat transfer fluids and energy storage materials. Rheological and wetting properties play an acute role in the handling and storage of materials and are closely related with pumping and corrosion issues. In this study the effect of nanoparticle addition on the aforementioned properties of molten Salt nanofluids is investigated. The Solar Salt (60% NaNO3 – 40% KNO3), as well as its individual components NaNO3 and KNO3, are mixed with various concentrations of SiO2. The contact angle and viscosity are measured throughout the liquid phase. Addition of a small percentage of nanoparticles, significantly alters the contact angle and viscosity of the nanofluid. In the absence of silica all the molten Salts display a linear behavior with respect to temperature. However, in the presence of nanoparticles the Solar Salt retains an elevated value until 300 °C in the case of the contact angle and 260 °C in the case of the viscosity, after which a steep reduction occurs. With larger concentrations of nanoparticles, this effect is shifted to higher temperatures. Similar behavior, however, is not present in the case of the NaNO3 and KNO3 individually, both of which, with the addition of nanoparticles, retain curve trends similar to their baseline cases. Further investigation, involving differential scanning calorimetry, suggests that nanoparticles delay the liquid/solid phase transition process of the molten Salt mixture, which in turn affects the rheological and wetting behavior of the molten mixture.

  • Molecular dynamics simulation of Solar Salt (NaNO3-KNO3) mixtures
    Solar Energy Materials and Solar Cells, 2019
    Co-Authors: Argyrios Anagnostopoulos, Alessio Alexiadis, Yulong Ding
    Abstract:

    Abstract Molten Salts have extended applications in concentrated Solar power (CSP) installations, both as heat transfer and energy storage materials. In this study, a set of Lennard-Jones interatomic parameters are introduced for simulating NaNO3 and KNO3, as well as their most frequently industrially used mixture the so-called Solar-Salt (60% NaNO3 – 40% KNO3). Local structures are studied via radial distribution functions. Furthermore, density, thermal conductivity, self-diffusivity, viscosity and surface tension are calculated, from melting to decomposition temperature, and compared with experimental data. The local structures are calculated with both existing and presented interatomic potentials and are found to be in excellent agreement. Additionally, density, viscosity and surface tension present minor differences from literature data. Thermal conductivity, in terms of absolute values is in the proximity of reported data but is questionable in terms of trend. Finally, self-diffusion coefficients declinate from measured values, but are similar in terms of trend. Results are found to be in good agreement. This work represents the first extended validated effort in modelling molten nitrate Salts and their mixtures at elevated temperatures using a Lennard-Jones potential, providing new tools that can aid in the fundamental understanding of molten Salt structures at the molecular scale.

  • rheology of Solar Salt based nanofluids for concentrated Solar power influence of the Salt purity nanoparticle concentration temperature and rheometer geometry
    Solar Energy Materials and Solar Cells, 2018
    Co-Authors: Belen Munozsanchez, Enrique J Julia, Javier Nietomaestre, Elisabetta Veca, Raffaele Liberatore, Salvatore Sau, Helena Navarro, Yulong Ding, Nuria Navarrete, Angel G. Fernández
    Abstract:

    Abstract Solar Salt-based nanofluids have attracted significant scientific interest in recent years due to their improved thermal properties, making them strong candidates as thermal energy storage materials and/or heat transfer fluids in CSP plants. There have been reports on increased specific heat due to the addition of nanoparticles, however, there is a lack of comprehensive information on other essential properties affecting the heat transfer, such as the viscosity. This article concerns the rheological behaviour of nanofluids made of Solar Salt (mass percentage at 60% NaNO 3 – 40% KNO 3 ) as the base fluid and silica or alumina nanoparticles as additives. The evolution of these nanofluids viscosity as a function of the shear rate (1–1000 s −1 ) at a temperature range of 250–400 °C was measured and analysed. The impact of the Salt purity (refined or industrial grade), the nanoparticle concentration (0.5–1.5 wt%) and the rheometer measuring configuration (coaxial cylinder or parallel plate) are examined. The results showed in general a Newtonian behaviour of the nanofluids with independency of the rheometer configuration. The relationship between the viscosity and the temperature follows an Arrhenius model. The influence of the nanoparticle concentration on the viscosity of the refined grade Solar Salt is analysed according to the Maron-Pierce and Kriegher-Dougherty models for the nanofluids containing alumina and silica nanoparticles respectively, due to their different shape.

  • Thermal and rheological behavior of Solar Salt containing highly thermally conductive particles
    2018
    Co-Authors: Anabel Palacios, Maria Elena Navarro, Yulong Ding
    Abstract:

    Nanofluids have arisen an interest in the last years given its high specific heat capacity and thermal conductivity. However, the lack of understanding of the underlying mechanism related to their behavior is still to be understood. In the present work, Solar Salt-based fluids were prepared by adding graphite particles with different geometries and particle size. The thermal conductivity and the viscosity were studied when adding 0.5%wt., 1%wt. and 1.5%wt. of nano-sized, micro-sized and flakes graphite. The main outcomes of the experimental work undertaken are that thermal conductivity and viscosity increment depends on morphology and particle size. However, they are not proportional and not concentration dependent. The results here obtained proved the need of identify the underlying mechanisms for properties performance among the fluids such as how particle size, morphology and content affects fluid properties.Nanofluids have arisen an interest in the last years given its high specific heat capacity and thermal conductivity. However, the lack of understanding of the underlying mechanism related to their behavior is still to be understood. In the present work, Solar Salt-based fluids were prepared by adding graphite particles with different geometries and particle size. The thermal conductivity and the viscosity were studied when adding 0.5%wt., 1%wt. and 1.5%wt. of nano-sized, micro-sized and flakes graphite. The main outcomes of the experimental work undertaken are that thermal conductivity and viscosity increment depends on morphology and particle size. However, they are not proportional and not concentration dependent. The results here obtained proved the need of identify the underlying mechanisms for properties performance among the fluids such as how particle size, morphology and content affects fluid properties.

  • Round robin test on the measurement of the specific heat of Solar Salt
    2017
    Co-Authors: Belén Muñoz-sánchez, Thomas Bauer, Javier Nieto-maestre, Alexander Bonk, Nuria Navarrete, Maria Elena Navarro, Jose Enrique Julia, José González-aguilar, Abdessamad Faik, Yulong Ding
    Abstract:

    Solar Salt (SS), a well-known non-eutectic mixture of sodium nitrate (60% w/w) and potassium nitrate (40% w/w), is commonly used either as Thermal Energy Storage (TES) material (double tank technology) or Heat Transfer Fluid (HTF) (Solar tower) in modern CSP plants worldwide. The specific heat (cp, kJ kg−1 °C−1) of SS is a very important property in order to support the design of new CSP Plants or develop novel materials based on SS. A high scientific effort has been dedicated to perform a suitable thermophysical characterization of this material. However, there is still a great discrepancy among the cp values reported by different authors1. These differences may be due to either experimental errors (random or systematic) or divergences in the starting material (grade of purity, presence of impurities and/or water). In order to avoid the second source of uncertainty (the starting material), a Round Robin Test (RRT) was proposed starting from a common material. In this way, the different methods from each ...

Enrique J Julia - One of the best experts on this subject based on the ideXlab platform.

  • rheology of Solar Salt based nanofluids for concentrated Solar power influence of the Salt purity nanoparticle concentration temperature and rheometer geometry
    Solar Energy Materials and Solar Cells, 2018
    Co-Authors: Belen Munozsanchez, Enrique J Julia, Javier Nietomaestre, Elisabetta Veca, Raffaele Liberatore, Salvatore Sau, Helena Navarro, Yulong Ding, Nuria Navarrete, Angel G. Fernández
    Abstract:

    Abstract Solar Salt-based nanofluids have attracted significant scientific interest in recent years due to their improved thermal properties, making them strong candidates as thermal energy storage materials and/or heat transfer fluids in CSP plants. There have been reports on increased specific heat due to the addition of nanoparticles, however, there is a lack of comprehensive information on other essential properties affecting the heat transfer, such as the viscosity. This article concerns the rheological behaviour of nanofluids made of Solar Salt (mass percentage at 60% NaNO 3 – 40% KNO 3 ) as the base fluid and silica or alumina nanoparticles as additives. The evolution of these nanofluids viscosity as a function of the shear rate (1–1000 s −1 ) at a temperature range of 250–400 °C was measured and analysed. The impact of the Salt purity (refined or industrial grade), the nanoparticle concentration (0.5–1.5 wt%) and the rheometer measuring configuration (coaxial cylinder or parallel plate) are examined. The results showed in general a Newtonian behaviour of the nanofluids with independency of the rheometer configuration. The relationship between the viscosity and the temperature follows an Arrhenius model. The influence of the nanoparticle concentration on the viscosity of the refined grade Solar Salt is analysed according to the Maron-Pierce and Kriegher-Dougherty models for the nanofluids containing alumina and silica nanoparticles respectively, due to their different shape.

  • increment of specific heat capacity of Solar Salt with sio2 nanoparticles
    Nanoscale Research Letters, 2014
    Co-Authors: Patricia Andreucabedo, L Hernandez, Raul Martinezcuenca, Luis Cabedo, Rosa Mondrago, Enrique J Julia
    Abstract:

    Thermal energy storage (TES) is extremely important in concentrated Solar power (CSP) plants since it represents the main difference and advantage of CSP plants with respect to other renewable energy sources such as wind, photovoltaic, etc. CSP represents a low-carbon emission renewable source of energy, and TES allows CSP plants to have energy availability and dispatchability using available industrial technologies. Molten Salts are used in CSP plants as a TES material because of their high operational temperature and stability of up to 500°C. Their main drawbacks are their relative poor thermal properties and energy storage density. A simple cost-effective way to improve thermal properties of fluids is to dope them with nanoparticles, thus obtaining the so-called Salt-based nanofluids. In this work, Solar Salt used in CSP plants (60% NaNO3+40% KNO3) was doped with silica nanoparticles at different solid mass concentrations (from 0.5% to 2%). Specific heat was measured by means of differential scanning calorimetry (DSC). A maximum increase of 25.03% was found at an optimal concentration of 1 wt.% of nanoparticles. The size distribution of nanoparticle clusters present in the Salt at each concentration was evaluated by means of scanning electron microscopy (SEM) and image processing, as well as by means of dynamic light scattering (DLS). The cluster size and the specific surface available depended on the solid content, and a relationship between the specific heat increment and the available particle surface area was obtained. It was proved that the mechanism involved in the specific heat increment is based on a surface phenomenon. Stability of samples was tested for several thermal cycles and thermogravimetric analysis at high temperature was carried out, the samples being stable.

  • increment of specific heat capacity of Solar Salt with sio2 nanoparticles
    Nanoscale Research Letters, 2014
    Co-Authors: Patricia Andreucabedo, Rosa Mondragon, L Hernandez, Raul Martinezcuenca, Luis Cabedo, Enrique J Julia
    Abstract:

    Thermal energy storage (TES) is extremely important in concentrated Solar power (CSP) plants since it represents the main difference and advantage of CSP plants with respect to other renewable energy sources such as wind, photovoltaic, etc. CSP represents a low-carbon emission renewable source of energy, and TES allows CSP plants to have energy availability and dispatchability using available industrial technologies. Molten Salts are used in CSP plants as a TES material because of their high operational temperature and stability of up to 500°C. Their main drawbacks are their relative poor thermal properties and energy storage density. A simple cost-effective way to improve thermal properties of fluids is to dope them with nanoparticles, thus obtaining the so-called Salt-based nanofluids. In this work, Solar Salt used in CSP plants (60% NaNO3 + 40% KNO3) was doped with silica nanoparticles at different solid mass concentrations (from 0.5% to 2%). Specific heat was measured by means of differential scanning calorimetry (DSC). A maximum increase of 25.03% was found at an optimal concentration of 1 wt.% of nanoparticles. The size distribution of nanoparticle clusters present in the Salt at each concentration was evaluated by means of scanning electron microscopy (SEM) and image processing, as well as by means of dynamic light scattering (DLS). The cluster size and the specific surface available depended on the solid content, and a relationship between the specific heat increment and the available particle surface area was obtained. It was proved that the mechanism involved in the specific heat increment is based on a surface phenomenon. Stability of samples was tested for several thermal cycles and thermogravimetric analysis at high temperature was carried out, the samples being stable. 65.: Thermal properties of condensed matter; 65.20.-w: Thermal properties of liquids; 65.20.Jk: Studies of thermodynamic properties of specific liquids

Ana García-romero - One of the best experts on this subject based on the ideXlab platform.

  • Compatibility of container materials for Concentrated Solar Power with a Solar Salt and alumina based nanofluid: A study under dynamic conditions
    Renewable Energy, 2020
    Co-Authors: Javier Nieto-maestre, Belén Muñoz-sánchez, Angel G. Fernández, Abdessamalk Faik, Yaroslav Grosu, Ana García-romero
    Abstract:

    Abstract Thermal energy storage (TES) is an efficient solution for improving the dispatchability of Concentrated Solar Power (CSP) plants. A system, consisting of two tanks with Solar Salt (NaNO3 60% wt. and KNO3 40% wt.) is commonly used. However, the investment cost of this technology is very high, due to the huge amount of Salts required (thousands of tons). A pronounced interest is evident for improving the thermophysical properties of molten Salts by adding small amounts of nanoparticles in order to reduce the mass of molten Salts at CSP. At the moment, the effect of nanoparticle addition on corrosion of container materials is poorly explored. In particular, there are no works regarding the dynamic effect of nanoparticles on the corrosivity of molten Salts. In this work we present first ever dynamic corrosion tests for Solar Salt doped with alumina nanoparticles (1% wt.). Carbon Steel A516 and SS347, used in double-tank system, were tested. Corrosion rates were 94.8 μm yr−1 and negligible respectively (1000 h, 385 °C). Detailed examination of construction materials revealed incorporation of nanoparticles into the corrosion layer and considerably lower corrosion rate as compared to the previously reported work on the nanoparticles-free Solar Salt.

  • A precise method to measure the specific heat of Solar Salt-based nanofluids
    Journal of Thermal Analysis and Calorimetry, 2017
    Co-Authors: Belén Muñoz-sánchez, Javier Nieto-maestre, Iñigo Iparraguirre-torres, Gorka Imbuluzqueta, Izaskun Marañón, Ana García-romero
    Abstract:

    A novel material has been developed for thermal energy storage at high temperatures (>300 °C) with enhanced thermal transport and storage properties. It is considered more efficient than the current molten Salts used in the concentrated Solar power plants. It is composed of an inorganic Salt doped with a small percentage of nanoparticles (NPs), which are claimed to increase the specific heat compared with that of the raw Salt. Thus, a precise determination of this thermal property is essential to perceive this enhancement. The specific heat of Solar Salt (SS) and a mixture of SS with 1 mass% of alumina NPs have been measured by the differential scanning calorimetry (DSC) technique. An isothermal procedure based on modulated DSC has been established to perform the measurements. The influence of the type of crucible, the amount of sample inside the crucible and the presence of moisture on the scattering of the data has been studied. Reliable results with a low uncertainty (

  • Preparation of nanofluids based on Solar Salt and boehmite nanoparticles: Characterization of starting materials
    2016
    Co-Authors: Belén Muñoz-sánchez, Javier Nieto-maestre, Iñigo Iparraguirre-torres, Jose Angel Sanchez-garcia, Jose Enrique Julia, Ana García-romero
    Abstract:

    A nanofluid composed of Solar Salt (SS) and boehmite nanoparticles (A) in a concentration of 1% by weight, is proposed as thermal storage medium for Concentrated Solar Power (CSP) plants. A wide characterization of the raw materials has been done, focused on their thermal stability and the nanoparticle primary size and shape among other properties such as its specific heat and crystalline structure. Some features of the final nanofluids have been also investigated: thermal stability, nanoparticle sizes and their distribution and specific heat. The showed results confirm that these materials are thermally stable in the working temperature range both individually and combined. In addition, the synthesis procedure implemented is effective to keep the nanoparticle sizes in the nanometric range (

  • The influence of mixing water on the thermophysical properties of nanofluids based on Solar Salt and silica nanoparticles
    2016
    Co-Authors: Belén Muñoz-sánchez, Javier Nieto-maestre, Iñigo Iparraguirre-torres, Jose Angel Sanchez-garcia, Jose Enrique Julia, Ana García-romero
    Abstract:

    The use of nanofluids (NFs) based on Solar Salt (SS) and nanoparticles (NPs), either as Thermal Energy Storage (TES) material or as Heat Transfer Fluid (HTF), is attracting great interest in recent years. Many authors [1,3] have reported important improvements on the thermophysical properties (specific heat capacity cp,thermal conductivity k) of NFs based on SS and ceramic NPs. These improvements would lead to important savings and better performance of TES facilities on new Concentrated Solar Power (CSP) plants due to lower quantities of material required and smaller storage tanks. To achieve these advantageous features in the final NFs, it is essential to avoid NP agglomeration during their preparation. Different synthesis procedures have been reported: mixing of solid NPs within a SS solution by means of ultrasounds [1-3], direct mixing of solid NPs and molten Salt [4]. In this work, NFs based on SS and 1% by wt. of silica NPs were synthetized from a SS-water solution and a commercial water-silica NF c...