Special Issue "Materials for Thermal Energy Storage"

A special issue of Applied Sciences (ISSN 2076-3417). This special issue belongs to the section "Energy".

Deadline for manuscript submissions: closed (31 July 2019).

Special Issue Editors

Dr. Luisa F. Cabeza
grade Website
Guest Editor
GREA Innovació Concurrent, Universitat de Lleida, Pere de Cabrera s/n, 25001 Lleida, Spain
Interests: thermal energy storage; building; energy efficiency; renewable energy; social acceptance of technologies; climate change mitigation
Special Issues and Collections in MDPI journals
Dr. Andrea Frazzica
Website SciProfiles
Guest Editor
Institute of Advanced Technologies for Energy, Italian National Council Research (CNR), 98126 Messina, Italy
Interests: development and characterization of materials and components for thermal energy storage and conversion; detailed models of heat and mass transfer in porous media; development of renewable heating and cooling solutions
Special Issues and Collections in MDPI journals

Special Issue Information

Dear Colleagues,

Thermal energy storage (TES) is becoming a key technology for the implementation of renewable energies in buildings and in industry, and also in increasing energy efficiency of our systems. Moreover, TES will clearly contribute in the decrease of CO2 emissions and climate change mitigation. However, TES systems need a good material selection. Moreover, available materials for TES applications need to be improved and enhanced. This Special Issue aims at gathering the best papers on development, improvement and enhancement of materials for TES. Materials for sensible, latent, sorption and chemical TES will be compiled

Prof. Luisa F. Cabeza
Dr. Andrea Frazzica
Guest Editors

Manuscript Submission Information

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Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 1800 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Published Papers (8 papers)

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Research

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Open AccessArticle
Combined Solar Thermochemical Solid/Gas Energy Storage Process for Domestic Thermal Applications: Analysis of Global Performance
Appl. Sci. 2019, 9(9), 1946; https://doi.org/10.3390/app9091946 - 12 May 2019
Abstract
Thermal energy used below 100 °C for space heating/cooling and hot water preparation is responsible for a big amount of greenhouse gas emissions in the residential sector. The conjecture of thermal solar and thermochemical solid/gas energy storage processes renders the heat generation to [...] Read more.
Thermal energy used below 100 °C for space heating/cooling and hot water preparation is responsible for a big amount of greenhouse gas emissions in the residential sector. The conjecture of thermal solar and thermochemical solid/gas energy storage processes renders the heat generation to become ecologically clean technology. However, until present, few pilot scale installations were developed and tested. The present work is devoted to the experimental study of global performance of a pilot scale thermochemical energy storage prototype. Two working modes, namely fixed packed bed and moving bed, were tested using 2.2 kg and 5.5 kg of composite material (silica gel impregnated with calcium chloride) under indoor atmospheric conditions. The global experimental efficiency of a 49l water tank charging process during 75 min was found as high as 0.8–0.85. The energy storage density reached in the fixed bed mode by the material was 158 kWh/m3, while in the moving bed mode it was 2.5 times lower. The reasons for such a difference are discussed in depth in the text. Full article
(This article belongs to the Special Issue Materials for Thermal Energy Storage)
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Open AccessArticle
Phase Diagrams of Fatty Acids as Biosourced Phase Change Materials for Thermal Energy Storage
Appl. Sci. 2019, 9(6), 1067; https://doi.org/10.3390/app9061067 - 14 Mar 2019
Cited by 5
Abstract
Thermal energy storage is known as a key element to optimize the use of renewable energies and to improve building performances. Phase change materials (PCMs) derived from wastes or by-products of plant or animal oil origins are low-cost biosourced PCMs and are composed [...] Read more.
Thermal energy storage is known as a key element to optimize the use of renewable energies and to improve building performances. Phase change materials (PCMs) derived from wastes or by-products of plant or animal oil origins are low-cost biosourced PCMs and are composed of more than 75% of fatty acids. They present paraffin-like storage properties and melting temperatures ranging from −23 °C to 78 °C. Therefore, they could be appropriate for latent heat storage technologies for building applications. Although already studied, a more detailed exploration of this class of PCMs is still required. In this frame, a screening of fatty acids and of their related binary systems must be performed. The infrared thermography method (IRT), already used for the fast estimation of simple phase diagrams (~2 h), appears to be best suited to achieve this goal. IRT method applicability to the more complex fatty acids phase diagrams is hence studied in this work. A phase diagram comprising more than a hundred data sets was obtained for the palmitic acid–stearic acid binary system. The reliability of the results is assessed by comparison to differential scanning calorimetry (DSC) measurements or results from other standard methods presented in literature and to a solid–liquid equilibrium thermodynamic model. Full article
(This article belongs to the Special Issue Materials for Thermal Energy Storage)
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Open AccessArticle
A Form Stable Composite Phase Change Material for Thermal Energy Storage Applications over 700 °C
Appl. Sci. 2019, 9(5), 814; https://doi.org/10.3390/app9050814 - 26 Feb 2019
Cited by 4
Abstract
Thermal energy storage (TES) is a highly effective approach for mitigating the intermittency and fluctuation of renewable energy sources and reducing industrial waste heat. We report here recent research on the use of composite phase change materials (PCM) for applications over 700 °C. [...] Read more.
Thermal energy storage (TES) is a highly effective approach for mitigating the intermittency and fluctuation of renewable energy sources and reducing industrial waste heat. We report here recent research on the use of composite phase change materials (PCM) for applications over 700 °C. For such a category of material, chemical incompatibility and low thermal conductivity are often among the main challenges. Our aims are to address these challenges through the formulation of form-stable composite PCMs and to understand their thermophysical properties. The eutectic K2CO3-Na2CO3 salt was used as a PCM with MgO as a form stabilizer. We found that such a formulation could maintain shape stability with up to 60 wt.% PCM. With a melting point of ~710.1 °C and an energy density as high as 431.2 J/g over a temperature range between 550 °C and 750 °C, the composite PCM was shown to be thermally stable up to 885 °C. An addition of 10 wt.% SiC enhanced the overall thermal conductivity from 1.94 W·m−1 K−1 to 2.28 W·m−1 K−1, giving an enhancement of 17.53%. Analyses of thermal cycling data also showed a high extent of chemical compatibility among the ingredients of the composite PCM. Full article
(This article belongs to the Special Issue Materials for Thermal Energy Storage)
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Open AccessArticle
Analysis of Bio-Based Fatty Esters PCM’s Thermal Properties and Investigation of Trends in Relation to Chemical Structures
Appl. Sci. 2019, 9(2), 225; https://doi.org/10.3390/app9020225 - 10 Jan 2019
Cited by 3
Abstract
As global energy demand increases while primary sources and fossil fuels’ availability decrease, research has shifted its focus to thermal energy storage systems as alternative technologies able to cover for the mismatch between demand and supply. Among the different phase change materials available, [...] Read more.
As global energy demand increases while primary sources and fossil fuels’ availability decrease, research has shifted its focus to thermal energy storage systems as alternative technologies able to cover for the mismatch between demand and supply. Among the different phase change materials available, esters possess particularly favorable properties with reported high enthalpies of fusion, low corrosivity, low toxicity, low supercooling, thermal and chemical stability as well as biodegradability and being derived from renewable feedstock. Despite such advantages, little to no data on the thermal behavior of esters is available due to low commercial availability. This study constitutes a continuation of previous works from the authors on the investigation of fatty esters as novel phase change materials. Here, methyl, pentyl and decyl esters of arachidic acid, and pentyl esters of myristic, palmitic, stearic and behenic acid are synthesized through Fischer esterification with high purities and their properties are studied. The chemical structures and purities are confirmed through Attenuated Total Reflectance Infrared Spectroscopy, Gas Chromatography coupled with Mass Spectroscopy and Nuclear Magnetic Resonance Spectroscopy, while the determination of the thermal properties is performed through Differential Scanning Calorimetry and Thermogravimetric Analysis. In conclusion, some correlations between the melting temperatures and the chemical structures are discovered, and the fatty esters are assessed based on their suitability as phase change materials for latent heat storage applications. Full article
(This article belongs to the Special Issue Materials for Thermal Energy Storage)
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Open AccessArticle
Mixed Metal Oxide Systems Applied to Thermochemical Storage of Solar Energy: Benefits of Secondary Metal Addition in Co and Mn Oxides and Contribution of Thermodynamics
Appl. Sci. 2018, 8(12), 2618; https://doi.org/10.3390/app8122618 - 14 Dec 2018
Cited by 6
Abstract
Thermochemical energy storage is promising for the long-term storage of solar energy via chemical bonds using reversible redox reactions. The development of thermally-stable and redox-active materials is needed, as single metal oxides (mainly Co and Mn oxides) show important shortcomings that may delay [...] Read more.
Thermochemical energy storage is promising for the long-term storage of solar energy via chemical bonds using reversible redox reactions. The development of thermally-stable and redox-active materials is needed, as single metal oxides (mainly Co and Mn oxides) show important shortcomings that may delay their large-scale implementation in solar power plants. Drawbacks associated with Co oxide concern chiefly cost and toxicity issues while Mn oxide suffers from slow oxidation kinetics and poor reversibility. Mixed metal oxide systems could alleviate the above-mentioned issues, thereby achieving improved materials characteristics. All binary oxide mixtures of the Mn-Co-Fe-Cu-O system are considered in this study, and their properties are evaluated by experimental measurements and/or thermodynamic calculations. The addition of Fe, Cu or Mn to cobalt oxide decreased both the oxygen storage capacity and energy storage density, thus adversely affecting the performance of Co3O4/CoO. Conversely, the addition of Fe, Co or Cu (with added amounts above 15, 40 and 30 mol%, respectively) improved the reversibility, re-oxidation rate and energy storage capacity of manganese oxide. Computational thermodynamics was applied to unravel the governing mechanisms and phase transitions responsible for the materials behavior, which represents a powerful tool for predicting the suitability of mixed oxide systems applied to thermochemical energy storage. Full article
(This article belongs to the Special Issue Materials for Thermal Energy Storage)
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Open AccessArticle
Synthesis and Investigation of Thermal Properties of Highly Pure Carboxylic Fatty Esters to Be Used as PCM
Appl. Sci. 2018, 8(7), 1069; https://doi.org/10.3390/app8071069 - 30 Jun 2018
Cited by 5
Abstract
Latent heat storage systems are gaining the attention of researchers as possible substitutes to conventional sensible heat storage systems due to their compactness and their ability to absorb and release heat almost isothermally. Among the Phase Change Materials (PCM) for energy storage studied [...] Read more.
Latent heat storage systems are gaining the attention of researchers as possible substitutes to conventional sensible heat storage systems due to their compactness and their ability to absorb and release heat almost isothermally. Among the Phase Change Materials (PCM) for energy storage studied so far, esters are believed to show promising properties. In particular, a broad range of melting temperatures, little to no supercooling, low corrosivity, chemical and thermal stability, and high enthalpies of fusion are reported. Many esters have the advantage of being bio-based and biodegradable, making them more sustainable in comparison to other popular PCM. Still, a clear lack of experimental data exists in regards to this class. In the present study, esters derived from saturated fatty carboxylic acids (myristic, palmitic, stearic, behenic), coupled with primary linear alcohols of different length (methanol, 1-decanol) were synthesized through Fischer esterification and their properties were investigated. Purities higher than 89% were obtained for all cases as proven by gas chromatography coupled with mass spectroscopy and nuclear magnetic resonance analysis. Additionally, the esters’ formation and reaction kinetics were characterized by attenuated total reflectance infrared spectroscopy. The esters produced showed to possess relatively high enthalpies of fusion above 190 J/g and thermal stability over three repeated cycles with differential scanning calorimetry. The melting points measured ranged between 20 °C and 50 °C, therefore proving to be interesting candidates for low-medium temperature applications such as heating and cooling in buildings. A correlation could be observed between the chemical structure and melting point of the produced esters. Additionally, thermogravimetric analysis revealed a higher thermal resistance for esters with longer aliphatic chains in comparison to shorter-chained ones. Full article
(This article belongs to the Special Issue Materials for Thermal Energy Storage)
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Open AccessArticle
Trouton’s Rule for Vapor Sorption in Solids
Appl. Sci. 2018, 8(4), 638; https://doi.org/10.3390/app8040638 - 20 Apr 2018
Cited by 1
Abstract
Hygroscopic salts exhibiting fast and reversible hydration are promising systems for seasonal heat storage, providing the possibility of storing excess solar energy from the warm season for later use during the cold season. For heat storage, the salt is dehydrated with the available [...] Read more.
Hygroscopic salts exhibiting fast and reversible hydration are promising systems for seasonal heat storage, providing the possibility of storing excess solar energy from the warm season for later use during the cold season. For heat storage, the salt is dehydrated with the available heat, and for heat recovery, the salt is rehydrated. There are many salt hydration transitions and for selecting the most suited ones with respect to the envisaged use cases, temperatures of dehydration and rehydration are needed, as well as the heat storage density. Estimation of these properties requires entropy and enthalpy changes of the transitions. Collections of hydration entropies and enthalpies have been published, but not all data seems reliable for various reasons, and it is often hard to access original sources and experimental conditions. For the necessary data validation, we propose the use of Trouton’s rule, known to hold for the evaporation of classes of fluids. Besides data validation, Trouton’s rule is useful for predicting heat storage densities and vapor pressures when only the transition enthalpy is known. We discuss the validity of Trouton’s rule for salt hydration and ammoniation transitions by theoretical and experimental evidence on the available extensive data collections. Full article
(This article belongs to the Special Issue Materials for Thermal Energy Storage)
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Review

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Open AccessReview
Mg-Based Hydrogen Absorbing Materials for Thermal Energy Storage—A Review
Appl. Sci. 2018, 8(8), 1375; https://doi.org/10.3390/app8081375 - 15 Aug 2018
Cited by 8
Abstract
Utilization of renewable energy such as solar, wind, and geothermal power, appears to be the most promising solution for the development of sustainable energy systems without using fossil fuels. Energy storage, especially to store the energy from fluctuating power is quite vital for [...] Read more.
Utilization of renewable energy such as solar, wind, and geothermal power, appears to be the most promising solution for the development of sustainable energy systems without using fossil fuels. Energy storage, especially to store the energy from fluctuating power is quite vital for smoothing out energy demands with peak/off-peak hour fluctuations. Thermal energy is a potential candidate to serve as an energy reserve. However, currently the development of thermal energy storage (TES) by traditional physical means is restricted by the relatively low energy density, high temperature demand, and the great thermal energy loss during long-period storage. Chemical heat storage is one of the most promising alternatives for TES due to its high energy density, low energy loss, flexible temperature range, and excellent storage duration. A comprehensive review on the development of different types of Mg-based materials for chemical heat storage is presented here and the classic and state-of-the-art technologies are summarized. Some related chemical principles, as well as heat storage properties, are discussed in the context. Finally, some dominant factors of chemical heat storage materials are concluded and the perspective is proposed for the development of next-generation chemical heat storage technologies. Full article
(This article belongs to the Special Issue Materials for Thermal Energy Storage)
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