Candidate For Thermal Energy Storage Research Articles

Synthesis and Characterization of the Paraffin/Expanded Perlite Loaded With Graphene Nanoparticles as a Thermal Energy Storage Material in Buildings

Abstract Various properties of the paraffin have made them compatible to be incorporated in the building materials for improving the latent heat storage capacity of the building envelope. However, the poor thermal conductivity of the paraffin reduces their thermal performance and hence limits their direct application/incorporation in the buildings. In this study, composite mixtures of paraffin and expanded perlite (EP) with an equal weight percent of 49.5 and 47.5, loaded with 1% and 5% of graphene nano-platelets, respectively, were synthesized. The developed samples were characterized uncycled and after 2000 thermal cycles. The results indicate that phase change material (PCM)/expanded perlite/graphene nano-platelets composite shows a significant increment in the thermal conductivity, reduction in the latent heat storage capacity, and a small weight loss. The heat storage/release test depicts that the phase change material/expanded perlite/graphene nano-platelets-5 shows 1.66 and 2.5 times faster heat storage/release rate than phase change material/expanded perlite/graphene nano-platelets-1 and paraffin, respectively. There is no significant change noted after 2000 thermal cycles in phase change material/expanded perlite/graphene nano-platelets-5 and phase change material/expanded perlite/graphene nano-platelets-1 samples, suggesting long-term reliability of the composite PCM. Additionally, thermogravimetric analysis (TGA) and Fourier-transform infrared spectroscopy (FTIR) testing were also conducted and the results suggest high thermal reliability and good chemical compatibility. These analyses suggest that the phase change material/expanded perlite/graphene nano-platelets composite can become a potential candidate for thermal energy storage.

Enhanced properties of diatomite-based composite phase change materials for thermal energy storage

Diatomite-based composite phase change materials (PCMs) with enhanced properties were prepared by vacuum impregnation method for thermal energy storage. Diatomite is used as a supporting matrix in composite PCMs due to its natural high porosity and relatively low price. Particularly, diatomite after microwave-acid treatment (Dm) with higher loading capability compared to raw diatomite was used as a supporting matrix to stabilize lauric acid-stearic acid (LA-SA). To improve the thermal conductivity of the composite PCMs, expanded graphite (EG) was introduced as a support matrix together with Dm at a weight ratio of 1:10 of EG to Dm. FTIR and XRD analysis indicated that the crystal structure of diatomite was not affected by the microwave-acid treatment and addition of EG, and no chemical reaction occurred between LA-SA and supports during impregnation. Devised LA-SA/Dm/EG with 72.2% loadage of LA-SA and a phase change temperature of 31.17 °C had latent heat value of 117.30 J g−1 for melting and 114.50 J g−1 for freezing, respectively. The thermal conductivity of LA-SA/Dm/EG was up to 3.2 times that of LA-SA/Dm. The thermal infrared images presented that the transient temperature response of LA-SA/Dm was enhanced after introducing of 2.5 wt% EG. Therefore, the prepared composite phase change material is a potential candidate for thermal energy storage in the indoor thermal comfort system, especially the building envelope.

Phase transitions in higher-melting imidazolium-based ionic liquids: Experiments and advanced data analysis

As thermal energy storage becomes an increasingly important topic, good knowledge of properties of phase-change materials (PCM) is essential. Among other properties, a good PCM should show a large enthalpy of melting, reproducible melting/solidification cycles, and long-term thermal stability. Temperatures and enthalpies of fusion should be determined at a possibly large range of conditions to allow for a critical evaluation of the experimental data and assessment of the material application potential.In this work, imidazolium-based ionic liquids (ILs) with long alkyl chain substituents 1-hexadecyl-3-methylimidazolium chloride and 1-hexadecyl-3-methyl-imidazolium saccharinate were studied in view of their possible use as phase-change materials. Differential scanning calorimetry (DSC) and the heat-leak modulus (HLM) methods were used to determine the temperatures and the enthalpies of phase transitions in the studied ILs, enabling us to study the influence of the heating and cooling rates on the measured properties. Enthalpies of fusion near to or larger than 100 J·g−1 were found in the studied ionic liquids, making them promising candidates for thermal energy storage. Peaks corresponding to possible liquid crystalline phases in the DSC traces of 1-hexadecyl-3-methylimidazolium saccharinate were observed, pointing to more complex phase behaviour of the studied ionic liquids.Finally, to critically evaluate the experimental data measured in this work, methods based on mathematical gnostics were used. Repeatability of measurements and the degree of mutual agreement between the methods used in this work could thus be determined.

Phase Transitions in Higher-Melting Ionic Liquids: Thermal Storage Materials or Liquid Crystals?

To assess the application potential of a material in thermal energy storage, the knowledge of their thermophysical properties is of key importance. Specifically, an efficient material has to show, among others, large enthalpies of phase change and a sufficiently large thermal conductivity.In this work, imidazolium-based ionic liquids (ILs) with long alkyl chain substituents 1-hexadecyl-3-methylimidazolium chloride and 1-hexadecyl-3-methylimidazolium saccharinate were studied in view of their possible use as phase-change materials. Differential scanning calorimetry (DSC) and the heat-leak modulus methods were used to determine the temperatures and the enthalpies of phase transitions in the studied ILs, enabling us to study the influence of the heating rates on the measured properties. Enthalpies of fusion near to or larger than 100 J·g–1 were found in the studied ionic liquids, making them promising candidates for thermal energy storage. Furthermore, peaks corresponding to possible liquid crystalline phases in the DSC traces of 1-hexadecyl-3-methylimidazolium saccharinate were observed.The measured properties are not only essential characteristics of a thermal storage material, temperatures and enthalpies of melting are necessary in thermodynamic description and modelling of solid-liquid phase behavior and thus in the possible utilization of the material in separation and crystallization processes.

Thermal and microstructural properties of paraffin/diatomite composite

The present work is devoted to the study of the impregnation of both the raw and calcined Algerian diatomite with a mixture of paraffin wax (PW) and liquid paraffin (LP) in order to obtain composite PCMs with a melting temperature below 30 °C and an appropriate latent heat. Structural, microstructural and thermal properties were studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT−IR), differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The raw diatomite contains many phases such as quartz (hexagonal SiO2), tridimite (trigonal SiO2) corundum (α-Al2O3, trigonal), CaSO4 (orthorhombic) and calcite (CaCo3, trigonal). After calcination, the main phases are quartz, tridimite, calcite and CaSO4. The SEM micrographs show that the PCMs are well impregnated into the diatomite pores. The FT−IR results reveal the absence of chemical interaction between paraffin and diatomite. The paraffin/calcined diatomite composite PCMs exhibits a melting temperature of 28.44 °C and a latent heat of about 56.40 J/g. Due to their thermal reliability and thermal energy storage performance after thermal cycling, the prepared composites PCMs are good candidates for thermal energy storage in buildings.

Experimental investigations of Alum/expanded graphite composite phase change material for thermal energy storage and its compatibility with metals

A novel composite phase change material(CPCM) were prepared with Aluminum potassium sulfate dodecahydrate(Alum, KAl(SO4)2·12H2O) as PCM and expanded graphite(EG) as nucleating agent and porous matrix for thermal conductivity enhancing. The detailed thermo-physical properties and thermal energy storage performance were studied. The DSC revealed that the melting temperature and latent heat of fusion of Alum/EG CPCM were 87.92 °C and 214.9J/g, respectively. The thermal conductivity of Alum/EG CPCM was improved from 0.497W·m−1·K−1 to 5.875W·m−1·K−1 due to the addition of EG, which can also be confirmed by the infrared thermal imager during charging/discharging process. The Alum/EG CPCM exhibited prominent chemical stability and thermal reliability before and after 500 thermal cycle tests. Furthermore, the corrosion of three metals and one metal alloy were studied and the gravimetric analysis and the results of element composition of four samples exhibited that the brass was the suitable materials for the container for long-term used while stainless steel 304L and aluminum were severely corroded. The results demonstrated that Alum/EG CPCM was a prospective candidate for thermal energy storage and accelerated the research on the Alum/EG heat storage system.

Superhydrophobic Copper Foam Supported Phase Change Composites with High Thermal Conductivity for Energy Storage

Superhydrophobic and superoleophilic oxidized copper foam (OCF) was prepared by oxidation of copper foam using (NH4)2S2O8 to generate rough surface then followed by modification with low surface energy substance polydimethylsiloxane (PDMS) and stearic acid (SA). Based on sperwetting, form-stable phase change materials (PCMs) composites were obtained by facile absorbing of organic PCMs into PDMS-OCF network. In this way, the organic PCMs can be spontaneously adsorbed and remain stable without leakage even at high temperature over their melting points, and the thermal storage capacity of the as-synthesized PCMs composites were analyzed using a differential scanning calorimeter (DSC). The latent heats of the PDMS-OCF/PCMs composites were measured to be 36.87 J g-1 and 36.81 J g-1 for PDMS-OCF/paraffin and PDMS-OCF/SA, respectively, which is greater than that of untreated copper form (CF)/paraffin composite (8.50 J g-1). The PDMS-OCF/PCMs composite shows better thermal stability and the loaded organic PCM has been reduced by 0.64% after 100 times of melting-cooling recycling for PDMS-OCF/paraffin. The thermal conductivity of PDMS-OCF/paraffin composite is about 9 times that of pure paraffin. Such excellent thermal conductivity as well as good thermal stability of the PDMS-OCF/PCMs makes it promising candidate for thermal energy storage.

Reactive Phase‐Change Materials for Enhanced Thermal Energy Storage

AbstractEffective storage and release of low‐to‐moderate temperature thermal energy (e.g., solar thermal or geothermal) could be transformational for applications such as space heating/cooling, domestic hot water, or off‐grid cooking. Good candidates for thermal energy storage in this temperature range include latent heat storage (LHS) systems and thermochemical energy storage (TCES) systems using reversible salt‐hydrate dehydration reactions. Here, we propose that an energy‐storage system by use of magnesium nitrate hexahydrate can potentially improve upon independent TCES or LHS systems by utilizing both the thermochemical hydration reaction and the latent heat available through the solid–liquid phase change of one magnesium nitrate hydrate eutectic. This chemistry is investigated through thermogravimetric analysis (TGA)/differential scanning calorimetry (DSC) analysis and shows a total energy density of approximately 1170±94 kJ kg−1 when dehydrating the material up to 145 °C. Reversible latent heat cycling at a eutectic melting temperature of 130 °C is shown by the DSC signal and estimated to be on the order of 115±9.2 kJ kg−1—a 10 % increase over the thermochemical energy storage alone. Although the latent energy release was found to decrease slightly over several cycles, the mass was found to stabilize near an asymptotic value corresponding to the published eutectic composition. These results suggest the concept of reactive phase‐change materials could be a promising solution to increasing the stored volumetric energy density.

Molecular Dynamics Simulations of the Thermal and Transport Properties of Molten NaNO<sub>2</sub>–NaNO<sub>3</sub> Systems

The thermodynamic and transport properties of nitrite and nitrate salts, which are candidates for thermal energy storage, were investigated by differential scanning calorimetry (DSC), high-temperature pulse-field NMR, and molecular dynamics (MD) simulations. The potential parameters of NO2 for the MD simulations were newly developed by ab initio calculations and empirical approaches. The MD results for molten xNaNO2–(1 − x)NaNO3 salts (x = 0, 0.2, 0.4, 0.6, 0.8, and 1.0) were comparable to the experimental density and Na self-diffusion coefficients. Moreover, the temperature-averaged heat capacities of the molten xNaNO2–(1 − x)NaNO3 systems were calculated from the changes in the energy and volume versus the temperature, which reproduced the results obtained from the DSC measurements well.

Improved Thermal Energy Storage Behavior of CuO/Palmitic acid Composite as Phase Change Material

The present work aims to study the preparation and thermal energy storage behavior of CuO based composite PCM for thermal energy storage. Composite PCM comprises palmitic acid as base material and CuO nanoparticles (NPs) as supporting materials. Different mass fractions of NPs have been dispersed in the base material so as to determine the maximum thermal conductivity enhancement. SDBS has been selected as the surfactant for ensuring the uniform dispersion of NPs in base material. With the help of DSC measurements, the newly prepared composite PCMs have been tested to determine their phase change temperatures as well as latent heats during melting and solidification. Thermal conductivities of the composite PCMs with all mass fractions of NPs have been measured. Based on the test results, the newly prepared composite PCM could be considered to be a potential candidate for thermal energy storage.

A proposition of peritectic structures as candidates for thermal energy storage

Peritectic structures are proposed as candidates for thermal energy storage in solar power plants. According to the evolution of Concentrated Solar Plants (CSP) technologies, the development of a new technology for ultra-compact Thermal Energy Storage (TES) over an extended range of temperatures is required. Identification, synthesis, analysis and characterization of innovative advanced materials should allow reaching outstanding energy density, long term stability, reasonable investment and could also enhancing heat transfers. All these assets make the ‘peritectics’ very appealing potential candidates for heat storage. In this work, a theoretical study based on phase diagrams modeling is performed to investigate the possible use of binary peritectic structures. It has been shown that peritectics can provide significantly increased energy density compared to simple melting/solidification processes, mainly because they involve chemical reactions. These materials could hence represent a very innovative and promising route for ultra-compact heat storage over a wide range of temperatures [300 - 700°C].

A review on system performance studies of aquifer thermal energy storage

Underground aquifer which consists of sand/water is considered as a good candidate for thermal energy storage due to its natural availability and large storage amount. Since the concept of aquifer thermal energy storage (ATES) was proposed, it has been accepted and constructed by many countries. The system performance of the ATES is of great interest for researchers. This paper intends to briefly review latest studies related to thermal performance and economic and environmental of ATES systems, especially these conducted since the year of 2010. The thermal performance indicators and their definitions were given. Available simulation methods for thermal performance evaluation and their characteristics were summarized. The review indicated that the thermal recovery ratio and the thermal interference intensity are the most commonly used indicators, and suitable thermal interference intensity should be decided to cost efficiently increasing energy provided in a given area. The energy saving of ATES systems could always amount to 40-90% while the payback time is always less than 5 years.

Enhanced thermal conductivity of waste sawdust-based composite phase change materials with expanded graphite for thermal energy storage

BackgroundWith the current rapid economic growth, demands for energy are progressively increasing. Energy shortages have attracted significant attention due to the shrinking availability of non-renewable resources. Therefore, thermal energy storage is one of the solutions that lead to saving of fossil fuels and make systems more cost-effective by the storage of wasted thermal energy. In particular, the application of phase change materials (PCMs) is considered as an effective and efficient approach to thermal energy storage because of the high latent heat storage capacity at small temperature intervals. Nevertheless, leakage problems and low thermal conductivity limit the practical applications of PCMs. Therefore, form-stable phase change materials with high thermal conductivity are urgently needed.ResultsA novel form-stable composite phase change material was prepared by incorporating PEG into waste sawdust with 5% EG. In the composites, PEG served as a phase change material, while waste sawdust acted as a carrier matrix. EG was added to help increase the thermal conductivity of the composites. The melting temperature of CPCMs-4 with 5% EG was found to be 58.6 °C with a phase change enthalpy of 145.3 kJ/kg, while the solidifying temperature was 48.5 °C with a phase change enthalpy of 131.4 kJ/kg. The thermal conductivity of CPCMs-4 with 5% EG increased by 23.8% compared with that of CPCMs-4. Moreover, no obvious changes in melting, solidifying temperature, or latent heat after 200 heating–cooling cycles were detected. The supercooling extent of CPCMs-4 with 5% EG decreased by 19.2% compared with PEG. The volume change properties and wettability properties of CPCMs-4 with 5% EG are suitable for thermal energy in terms of practical application.ConclusionsThe prepared composites have excellent thermal and form-stable properties and they can be recognized as potential candidates for thermal energy storage as form-stable composite phase change materials. Using simple impregnation techniques with waste sawdust as a supporting material, this study demonstrates an innovative technology for practically and markedly enhancing the adsorption capacity of phase change materials.

Preparation and Characterization of Graphene Oxide‐Grafted Hexadecanol Composite Phase‐Change Material for Thermal Energy Storage

AbstractWith the aim of improving the shape stability and recycling reliability of hexadecanol (HD), graphene oxide (GO)‐grafted hexadecanol (GO‐g‐HD) shape‐stabilized phase‐change material (SSPCM) with good thermochemical properties was prepared by oxidizing graphite powders to form GO, which was converted into the acyl chloride and finally condensed with HD. Various characterization techniques were employed to investigate the microstructure, thermal properties, thermal durability, and reliability of the composite. The results show that HD was embedded in the composite with a maximum mass fraction of 62.7 wt % through physical adsorption and covalent bonding. The grafted percentage and density of HD on ultrathin GO sheets are 36.5 wt % and 1.51 mmol g−1, respectively. The GO‐g‐HD SSPCM melts at 49.7 °C with a latent heat of 152.3 J g−1, and freezes at 45.4 °C with a phase‐change enthalpy of 129.9 J g−1. The thermal conductivity of GO‐g‐HD is measured as 0.519 W m−1 K−1, which is an improvement of 41.8 % compared with that of neat HD. Moreover, the as‐prepared composite also presents excellent chemical and thermal stability, excellent thermal durability, negligible variation in latent heats, and no changes in the phase‐change temperatures due to strong covalent bonds and interactions between the matrix and HD. Thus, GO‐g‐HD is a promising candidate for thermal energy storage in the future because of the very good latent heat, enhanced conductivity, and stability.

Microencapsulation of stearic acid with polymethylmethacrylate using iron (III) chloride as photo-initiator for thermal energy storage

Abstract Aiming to identify the validity of fabricating microencapsulated phase change material (PCM) with polymethylmethacrylate (PMMA) by ultraviolet curing emulsion polymerization method using iron (III) chloride as photoinitiator, SA/PMMA microcapsules were prepared and various techniques were employed to determine the ignition mechanism, structural characteristics and thermal properties of the composite. The results shown that the microcapsules containing SA with maximum percentage of 52.20 wt% formed by radical mechanism and only physical interactions existed in the components both in the prepared process and subsequent use. The phase change temperatures and latent heats of the microencapsulated SA were measured as 55.3 °C and 102.1 J·g − 1 for melting, and 48.8 °C and 102.8 J·g − 1 for freezing, respectively. Thermal gravimetric analysis revealed that SA/PMMA has good thermal durability in working temperature range. The results of accelerated thermal cycling test are all shown that the SA/PMMA have excellent thermal reliability and chemical stability although they were subjected 1000 melting/freezing cycles. In summary, the comparable thermal storage ability and good thermal reliability facilitated SA/PMMA to be considered as a viable candidate for thermal energy storage. The successful fabrication of SA/PMMA capsules indicates that ferric chloride is a prominent candidate for synthesizing PMMA containing PCM composite.

Thermodynamic assessment of binary systems Tris(hydroxymethyl)aminomethane-Pentaglycerine (TRIS-PG) and 2-amino-2-methyl-1,3-propanediol-Pentaglycerine (AMPL-PG) phase diagrams

Solid state phase change materials are considered as potential candidates for thermal energy storage. Among the solid–solid heat storage materials, the most promising heat storage materials are organic polyalcohol globular tetrahedral molecular crystals such as (CH3)C(CH2OH)3 for PG, (NH2)C(CH2OH)3 for TRIS, and (CH3)(NH2)C(CH2OH)2 for AMPL, which store a large amount of thermal energy in their solid state high temperature phases with orientationally disorder crystal structure. In this study, we obtained the Gibbs energies of pure PG and pure TRIS derived utilizing the available experimental data including temperature-dependency of heat capacity, enthalpy, and transitions temperatures, as well as obtained optimized binary phase diagrams of TRIS-PG and AMPL-PG by CALPHAD calculations. The phase boundaries are verified by in-situ X-ray diffraction (XRD). Optimized database of these two binaries will allow exploration of ternary and higher order systems using CALPHAD methodology that will provide a wider selection of materials for practical thermal energy storage applications. Regular and sub-regular solution models are used for calculations in which the excess Gibbs energies are expressed by the Redlich–Kister–Muggianu polynomial. A set of self-consistent interaction parameters formulating the Gibbs energies of various phases in binary systems are obtained. The TRIS-PG binary phase diagram was calculated from room temperature to the liquid phase temperature, the modeled phase diagram and the experimental data from our work are in good agreement. We also used experimental data of TRIS-PG from the literature which shows a good agreement between the two data sets. Our optimized TRIS-PG phase diagrams show a wider solid-state two phase region, where there is de-mixing of phases, whereas the calculations from the literature show a very narrow region. We also present optimized AMPL-PG binary phase diagram using PARROT module in Thermal-Calc software. The calculated phase diagrams for the two systems mentioned above are presented along with the experimental data.

Influence of accelerated thermal charging and discharging cycles on thermo-physical properties of organic phase change materials for solar thermal energy storage applications

Integration of appropriate thermal energy storage system plays a predominant role in upgrading the efficiency of solar thermal energy devices by reducing the incongruity between energy supply and demand. Latent heat thermal energy storage based on phase change materials (PCM) is found to be the most efficient and prospective method for storage of solar thermal energy. Ensuring the thermal reliability of PCM through large number of charging (melting) and discharging (solidification) cycles is a primary prerequisite to determine the suitability of PCM for a specific thermal energy storage applications. The present study explains the experimental analysis carried out on two PCM’s namely benzamide and sebacic acid to check the compatibility of the material in solar thermal energy storage applications. The selected materials were subjected to one thousand accelerated melting and solidification cycles in order to investigate the percentage of variation at different stages on latent heat of fusion, phase transition temperature, onset and peak melting temperature. Differential Scanning Calorimeter (DSC) was used to determine the phase transition temperature and heat of fusion upon completion of every 100 thermal cycles and continued up to 1000 cycles. Relative Percentage Difference (RPD%) is calculated to find out the absolute deviation of melting temperature and latent heat of fusion with respect to zeroth cycle. The experimental study recorded a melting temperatures of benzamide and sebacic acid as 125.09°C and 135.92°C with latent heat of fusion of 285.1(J/g) and 374.4(J/g). The maximum RPD for melting temperature and heat of fusion for benzamide was calculated as 0.02% and −14.83% whereas sebacic acid it was −0.85% and −6.06% upon 1000 thermal cycles. The study revealed that both benzamide and sebacic acid are potential candidates for thermal energy storage due to their superior thermal reliability characteristics even after one thousand thermal cycles.

Fabrication and characterization of stearic acid/polyaniline composite with electrical conductivity as phase change materials for thermal energy storage

This paper presents the experimental investigation on the thermal properties and electrical conductivity of the new microencapsulated phase change material by entrapping of stearic acid (SA) into PANI (polyaniline) shell through self-assembly method. Experimental results reveal that PANI nuclei grew on the surface of SA, and then copied its original morphological structure and finally exhibited peony flower-like morphology. The two components have good compatibility and have no chemical reaction both in the process of fabrication and subsequent use, while hydrogen bondings between the imino groups and carboxyl groups exist. The maximum mass fraction of stearic acid loaded in SA/PANI is determined as high as 62.1wt% without seepage of melted SA from capsules. Due to the secondary doping with carboxyl group, the composite phase change material embedded with SA exhibits improved electrical conductivity from 0.3968Scm−1 to 0.7042Scm−1 when compared to PANI. The phase change temperatures and latent heats of SA/PANI are measured to be 55.6°C and 113.02J/g for melting and, 50.8°C and 112.58J/g for freezing, respectively. TG analysis test revealed that the prepared SA/PANI composite PCM has high thermal durability in working temperature range. Moreover, the results of DSC, FT-IR, TG, conductivity investigation and thermal cycling test are all show that the thermal reliability and electrical conductivity of the SA/APNI have imperceptible changes. In total, the additional electrical conductivity, high heat storage potential and good thermal reliability and stability facilitated SA/PANI to be considered as a viable candidate for thermal energy storage, antistatic thermo-regulating textiles and other applications.

Effect of Graphene Layer Thickness and Mechanical Compliance on Interfacial Heat Flow and Thermal Conduction in Solid–Liquid Phase Change Materials

Solid-liquid phase change materials (PCMs) are attractive candidates for thermal energy storage and electronics cooling applications but have limited applicability in state-of-the-art technologies due to their low intrinsic thermal conductivities. Recent efforts to incorporate graphene and multilayer graphene into PCMs have led to the development of thermal energy storage materials with remarkable values of bulk thermal conductivity. However, the full potential of graphene as a filler material for the thermal enhancement of PCMs remains unrealized, largely due to an incomplete understanding of the physical mechanisms that govern thermal transport within graphene-based nanocomposites. In this work, we show that the number of graphene layers (n) within an individual graphene nanoparticle has a significant effect on the bulk thermal conductivity of an organic PCM. Results indicate that the bulk thermal conductivity of PCMs can be tuned by over an order of magnitude simply by adjusting the number of graphene layers (n) from n = 3 to 44. Using scanning electron microscopy in tandem with nanoscale analytical techniques, the physical mechanisms that govern heat flow within a graphene nanocomposite PCM are found to be nearly independent of the intrinsic thermal conductivity of the graphene nanoparticle itself and are instead found to be dependent on the mechanical compliance of the graphene nanoparticles. These findings are critical for the design and development of PCMs that are capable of cooling next-generation electronics and storing heat effectively in medium-to-large-scale energy systems, including solar-thermal power plants and building heating and cooling systems.

Characterization of Several Moroccan Rocks Used as Filler Material for Thermal Energy Storage in CSP Power Plants

This paper demonstrates the potential of the quartzite as an economic and efficient filler material in thermal oil direct thermocline storage system. This natural rock appears as a good candidate for thermal energy storage by sensible heat up to 350°C.In the present study, many experiences were conducted in order to choose the best rock among five varieties (quartzite, basalt, granite, hornfels and marble) which are found abundant in Morocco. The optimal rock was selected according to various criteria such as surface characteristics, porosity, density, calorific capacity, hardness, mechanical resistance. The chosen rock should also provide a thermal stability during energy exchange with the heat transfer fluid (HTF). It should be noted that choice of the rocks as a filler material may reduce the quantity of the HTF used for charging and discharging the thermal energy. Hence, the shrinkage of tank volume by thermocline sensible heat storage system using rocks as filler materials allows reducing the cost with an increase in the efficiency of the system.