Thermal Energy Storage Capability Research Articles

Study on thermal energy storage properties of bio-based n-dodecanoic acid/fly ash as a novel shape-stabilized phase change material

In the present study, a novel BSPCM was prepared with the n-dodecanoic acid (or) LA phase change material, which was vacuum impregnated into the porous FA pebbles. The surface morphology of the BSPCM has confirmed the presence of the lauric acid in the porous supporting matrix. The XRD analysis of the BSPCM revealed that the crystalline nature of the PCM was unaltered after impregnation. The surface structure study verified the chemical compatibility between the PCM and supporting material. The DSC results showed that, BSPCM has exhibited a good latent heat of fusion of 68.93 kJ/kg with high thermal energy storage capability of 97.62%. The BSPCM was thermally stable up to 150 °C and showed good leakage stability up to 85 °C. Thermal reliability of the BSPCM performed for 1000 thermal cycles revealed excellent thermal reliability index of 96.76%. Further, thermal conductivity of BSPCM was found to be 0.1702 W/mK, which was attributed to the effective impregnation of the PCM into the fly ash pebbles. In total, the developed BSPCM can be a viable candidate for achieving passive thermal energy storage in buildings.

Advanced 3D-printed phase change materials

Advanced 3D-printed phase change materials

On-Sun Testing of a High-Temperature Solar Receiver’s Flux Distribution

Abstract Concentrated solar power (CSP) is a promising technology in transitioning to renewable energy because of its abundance in nature and thermal energy storage (TES) capability. Among the four types of available CSP technology, including parabolic trough, linear Fresnel, power tower, and parabolic dishes, a power tower using a central receiver has more potential to generate high-temperature heat in a scale supporting power cycles efficiency and achieve low levelized cost of energy (LCOE). Other than the conventional type of receiver design, the high-absorptive receiver concept developed and presented in this paper is novel in its design approach. The novel receiver design originated from National Renewable Energy Laboratory (NREL) consists of an array of solar flux absorb tubes. The solar absorb tubes require uniform flux distribution and in-depth flux penetration through the three different reflective sections of tubes in a hexagonal shape. To evaluate this unique receiver design and thermal performance, the flux distribution, flux uniformity, and intensity were numerically simulated using ansys fluent and SolTrace modeling program. On-sun testing has been done at NREL high flux solar testing facility, based on the computational analysis.

Morphology-controlled fabrication of magnetic phase-change microcapsules for synchronous efficient recovery of wastewater and waste heat

Contamination and waste heat are major issues in water pollution. Aiming at efficient synchronous recovery wastewater and waste heat, we designed a novel CaCO3-based phase-change microcapsule system with an n-docosane core and a CaCO3/Fe3O4 composite shell. The system was fabricated through an emulsion-templated in situ precipitation approach in a structure-directing mode, resulting in a controllable morphology for the resultant microcapsules, varying from a peanut hull through ellipsoid to dumbbell shapes. The system has a significantly enlarged specific surface area of approximately 55 m2·g−1 with the CaCO3 phase transition from vaterite to calcite. As a result, the microcapsule system exhibits improved adsorption capacities of 497.6 and 79.1 mg/g for Pb2+ and Rhodamine B removal, respectively, from wastewater. Moreover, increase in the specific surface area of the microcapsule system with a sufficient latent heat capacity of approximately 130 J·g−1 also resulted in an enhanced heat energy-storage capability and thermal conductance for waste-heat recovery. The microcapsule system also exhibits a good leakage-prevention capability and good multicycle reusability owing to the tight magnetic CaCO3/Fe3O4 composite shell. This study provides a promising approach for developing CaCO3-based phase-change microcapsules with enhanced thermal energy storage and adsorption capabilities for efficient synchronous recovery of wastewater and waste heat.

Development of textile nanocomposites with thermal energy storage capability

In this study, textile-based composites with dynamic heat storage capability have been designed and developed, in addition to their existing passive insulation capacity. First, poly(acrylonitrile) (PAN) shell and poly(ethylene glycol) (PEG1000 or PEG1500) cores are produced by coaxial electrospinning. Then, these are incorporated into felt based composite structures, which demonstrate enhanced thermal properties as well as buffering function against temperature changes in the environment. The thermal energy absorption and release capacities of the felt composites including PAN-PEG1000 or PAN-PEG1500 nanowebs are measured as high as 81 Jg -1 between 33 oC and 46 oC, and 48 Jg -1 between 46 oC and 54 oC respectively. Felt composites, combined with PAN-PEG nanowebs offer forthcoming production applications in the field of dynamic thermal management in various industries.

Mechanical Behaviour of Multifunctional Epoxy/Hollow Glass Microspheres/Paraffin Microcapsules Syntactic Foams for Thermal Management.

Epoxy/hollow glass microsphere (HGM) syntactic foams (SFs) are peculiar materials developed to combine low density, low thermal conductivity, and elevated mechanical properties. In this work, multifunctional SFs endowed with both structural and thermal management properties were produced for the first time, by combining an epoxy matrix with HGM and a microencapsulated phase change material (PCM) having a melting temperature of 43 °C. Systems with a total filler content (HGM + PCM) up to 40 vol% were prepared and characterized from the mechanical point of view with a broad experimental campaign comprising quasi-static, impact, and fracture toughness tests. The experimental results were statistically treated and fitted with a linear model, to produce ternary phase diagrams to provide a comprehensive interpretation of the mechanical behaviour of the prepared foams. In quasi-static tests, HGM introduction helps to retain the specific tensile elastic modulus and to increase the specific compressive modulus. The brittle nature of HGMs decreases the Charpy impact properties of the SFs, while the PCM insertion improve their toughness. This result is confirmed in KIC and GIC tests, where the composition with 20 vol% of PCM shows an increase of 80% and 370% in KIC and GIC in to neat epoxy, respectively. The most promising compositions are those combining PCM and HGMs with a total particle volume fraction up to 40 vol%, thanks to their optimal combination of thermal management capability, lightness, thermal insulation, and mechanical properties. The ability to fine-tune the properties of the SFs, together with the acquired thermal energy storage (TES) capability, confirm the great potential of these multifunctional materials in automotive, electronics, and aerospace industries.

Phase‐change composites silicone rubber/paraffin@ SiO 2 microcapsules with different core/shell ratio for thermal management

A series of paraffin (Pa)@silicon dioxide (SiO2) microcapsules with different core/shell ratios were constructed by interfacial-polycondensation of tetraethoxysilane (TEOS) and γ-Methacryloxypropyltrimethoxysilane (MPS), and then were embedded in addition-cure liquid silicone rubber (ALSR) to fabricate ALSR/Pa@SiO2 phase-change composites. The SiO2 shell can avoid the leakage of Pa. Meanwhile, the in-situ modification of the SiO2 shell by MPS can enhance the interface bonding between Pa@SiO2 and ALSR, because the C═C bond introduced by MPS on the SiO2 shell can participate in the curing reaction of ALSR. The study explored the effects of the core/shell ratio on the Pa@SiO2 microcapsules and ALSR/Pa@SiO2 composites. Differential scanning calorimetry analysis demonstrated that ALSR/Pa@SiO2 composites have dependable thermal energy storage capability which can reach to 90.7 J g−1 and phase-change enthalpy of the composites increase with the core/shell ratio. The ALSR/Pa@SiO2 composites were found as form-stable phase-change materials with low leakage rate, which is attributed to the protection of both SiO2 shell and ALSR matrix. Due to the chemical interfacial interaction, the composites displayed improved mechanical strength. The composites can be used for thermal management and temperature regulation as an electronic packaging material.

Modeling the thermal energy storage capability of a phase change material confined in a rectangular cavity

Phase change materials (PCM) may be used as a thermal energy barrier for applications requiring insulation. This project explores the behavior of pure PCM within a two-dimensional rectangular cavity as a thermal barrier using a new thermal barrier efficiency metric. The dimensionless parameters are determined that dictate the efficiency for one-dimensional transport with cyclical heat flux loading on one side and a convective boundary condition on the opposite side. Two limiting conditions for the PCM behavior (No Phase Change and Full Phase Change) are studied analytically, and numerical models show that the predicted thermal barrier efficiency exceeds these limits, suggesting that the limiting conditions provide useful conservative estimates of PCM performance in designing PCM thermal barriers. Results show that both the No Phase Change limit and Full Phase Change efficiencies decrease with increasing Fourier and decreasing Biot numbers. An expression is derived for the CFD-predicted thermal barrier efficiency as a function of No Phase Change and Full Phase Change efficiencies and the Fourier number when Bi = 0.2.

Nanofluid-PCM heat sink for building integrated concentrated photovoltaic with thermal energy storage and recovery capability

A new configuration of phase change material (PCM) heat sink has been developed to be combined with a building integrated concentrated photovoltaic (BICPV) system. This new proposed system includes PCM encapsulated in aluminum pack and immersed in nanofluid container to improve thermal conductivity. A comprehensive numerical model was validated and simulated to evaluate thermal and electrical performance of the proposed system for both passive and active cooling conditions. Two different configurations of nanofluid-PCM enclosures with single PCM pack or multi-smaller packs were compared with conventional BICPV-PCM system. Melting and solidification of PCM were also studied with solar concentration ratio of 5. In passive cooling, single-pack configuration regulated the silicon temperature of CPV below 78 °C with more uniform temperature distribution. Whereas the multi-packs configuration demonstrated 97% phase transition to liquid PCM which provided the highest stored thermal energy. The performance improvement would be attributed to the enhancement of thermal conductivity and natural convection of nanofluid in PCM container. Furthermore, in active cooling condition, the silicon temperature controlled under 43 °C with uniform distribution. The nanofluid flow could be solidified up to 97% and 90% of initially melted PCM after 60 min for multi-packs and single-pack configurations, respectively.

Facile technique to encapsulate phase change material in an amphiphilic polymeric matrix for thermal energy storage

A facile fabrication technique of producing novel porous microcapsules encapsulating n-Eicosane as phase change material (PCM) with a random copolymer of poly (methyl methacrylate0.9-co-2-hydroxyethyl methacrylate0.1) (poly(MMA0.9-co-HEMA0.1)) as shell material is being reported. The porous microparticles (particle size: 31.8 ± 9 µm; porosity: ~30 ± 13%) with a hollow core (shell thickness: 1.60 ± 0.2 µm) were obtained by adopting a synthetic pathway of hot water assisted double emulsion (water/oil/water) system. Strikingly, the microcapsule system was found to entrap > 95% n-Eicosane, thus achieving significantly high thermal energy storage capability (~95%). The porous microcapsules with a phase transition enthalpy of ~ 160 J/g exhibited high phase transfer repeatability and long durability. The non-isothermal and isothermal DSC study further revealed the heat charging and discharging conditions for the microcapsules. Moreover, in contrast to neat hydrophobic PCM, the porous particles with partially hydrophilic shell (owing to polyHEMA unit) displayed better water dispersibility along with efficient thermal management characteristic as revealed by Infrared thermography. Thus, the microencapsulated phase change material in porous microcapsules can be a smart combination of good thermal energy storage function with wettability. Potentially such microcapsules may be exploited as thermal energy storage materials for space conditioning in buildings because of the suitable phase transition temperature (37 °C) displayed by the selected PCM (n-Eicosane). Our study comprehensively demonstrated water dispersible porous polymeric particles with significantly high thermal energy storage (>95%) performance that was not reported till date.

Internal insulation and corrosion control of molten chloride thermal energy storage tanks

A chloride-based molten-salt system that uses a ternary blend of MgCl2/KCl/NaCl is investigated to provide higher-temperature thermal energy storage capability than conventional nitrate salt-based systems. Despite their high thermal stability and operating temperature, molten chlorides present several challenges, including the design of internal liners to prevent the corrosion and thermal stress of alloy tank shells. This work discusses issues and potential solutions related to containment of molten chloride salt, specifically the optimization of the hot face refractory materials for use as internal liners. Three down-selected refractory materials were analyzed with respect to permeation of salt through the material as well as chemical stability during high temperature operation. Through the application of X-ray imaging and electron spectroscopy techniques, highly stable secondary surface phases in equilibrium with the molten salt were identified, as well as time-dependent changes in the salt composition itself.

Enhanced workability, durability, and thermal properties of cement-based composites with aerogel and paraffin coated recycled aggregates

The use of construction and demolition (C&D) wastes in building materials is a key step toward a sustainable construction industry. In this context, the application of recycled concrete aggregates (RCAs) in cement composite mixtures has been investigated by various researchers. The results available in the literature indicate that cement mortar adhered to the surface of RCAs leads to high water absorption and large porosity in cementitious mixtures. As a result, lower workability, durability, and mechanical properties in comparison to conventional aggregates are often known as the main attributes of mixtures containing RCAs. Additionally, improving the thermal energy storage capability of RCAs by using high-performance thermal insulation materials, such as phase change materials (PCMs) and aerogel can assist in minimizing the energy consumption in buildings. Accordingly, this paper aims at characterizing RCA mixtures with enhanced workability, durability, and thermal properties. The effect of using paraffin coated recycled concrete aggregates (PCRAs) and aerogel aggregates on the mechanical, thermal, and durability properties of cement composites are investigated in this paper. Results of dry density, compressive strength, water absorption content, permeable voids, thermal conductivity, rapid chloride migration test (RCMT), capillary water absorption, and scanning electron microscopy (SEM) tests along with energy-dispersive X-ray spectroscopy (EDX) are reported to evaluate the effect of several variables on the investigated concrete mixtures. Results of the conducted tests indicate that using PCRA significantly improves the durability characteristics of mixtures such as water absorption content, permeable voids, and RCMT, while it slightly decreases the compressive strength of mixtures with respect to the control mixture. In addition, aerogel aggregates significantly improve the thermal conductivity of mixtures while reduced the mechanical and durability characteristics.

Copper Sulfide Nanodisk-Doped Solid–Solid Phase Change Materials for Full Spectrum Solar-Thermal Energy Harvesting and Storage

Phase change materials (PCMs) provide a state-of-the-art thermal energy storage capability and offer enormous potential for solar energy storage systems. However, the widespread adaptation of PCMs in advanced energy systems is often limited by low energy harvesting efficiency and poor shape stability. Thus, developing shape-stable PCMs for high-efficiency solar-thermal energy storage has remained an impediment to further advancement. Herein, we devised novel shape-stable composite PCMs based on monodispersed CuS disk-like nanoparticles and solid-solid PCM polyurethane (PU). In our devised composite system, the incorporated CuS nanoparticles act as a photonic nanoheater and the PU matrix acts as the heat reservoir which can store thermal energy via the latent heat while the phase transition occurs. The fabricated CuS@PU composite with 4 wt % doping of CuS nanodisks exhibits a phase change enthalpy of around 120 J/g, which is only 14% lower than that of the neat PU PCM. Owing to the solid-state phase transition of the PU PCM, only 0.6% of energy storage loss occurred over 100 repeated heating and cooling cycles. Besides, the solar-thermal energy storage efficiency of the CuS@PU composite exceeds 92% at 1 sun illumination under the full solar spectrum. Based on these outstanding thermophysical properties such as excellent shape stability, thermal stability, and thermal reliability, the developed CuS@PU composite PCMs are imperative candidates for real-world applications.

Ti3C2Tx@Polyvinyl alcohol foam-Supported Phase Change Materials with Simultaneous Enhanced Thermal Conductivity and Solar-Thermal Conversion Performance

The phase change materials (PCMs) are attractive and environmental-friendly way to improve the utilization rate in the field of photothermal conversion and solar radiation storage. However, the low photothermal conversion efficiency and low thermal conductivity characteristics of PCMs limit their practical applications. In order to improve the performance of these materials, we developed a novel polyethylene glycol (PEG 2000) PCMs composites supported by Ti3C2Tx@polyvinyl alcohol (PVA) foam skeleton with several advantages like low-cost, scalable and simple preparation method by freeze-drying after PEG being introduced into the skeleton via vacuum impregnation. The thermal conductivity of Ti3C2Tx/PEG composite containing 7.68 wt% skeleton was notably high as 0.428 W/(m·K)，which was 4.2 times higher than PEG 2000 (0.101 W/(m·K)). The improvement of thermal conductivity was mainly derived from the three-dimensional interconnected structures of the foamy skeleton. The actual phase change enthalpy of composite searched up to 131.1 J/g, and its photothermal conversion efficiency achieved 96.5%, demonstrating excellent photothermal conversion and storage ability. Furthermore, the Ti3C2Tx/PEG composite exhibited structural stable property that avoids leakage of liquefied PCM during melting process. This multifunctional Ti3C2Tx@PVA/PEG PCM provided a prospective application in thermal energy management systems regarding its high thermal conductivity, excellent photothermal conversion efficiency, thermal energy storage (TES) capability and structural stability.

Eutectic composition of selected phase change materials for thermal energy storage applications

Latent heat storage in salt mixture has drawn so much attention because of the salt mixture’s capability of storing large quantity of heat when compared to single salt thereby, making it more feasible for use as phase change material. However it is worthwhile to find out among various combination of salts forming eutectic mixtures, the one that has the best energy storage capability by evaluating and comparing their melting points and latent heat storage. So in this research work, four different types of eutectic mixture of salts were prepared and experimentally investigated for the best thermal energy storage capability. The first eutectic mixture consists of 2.6g of LiNO3, 6.4g of NH4NO3 and 1g of NaNO3. The second eutectic mixture consists of1.75g of LiNO3, 3.9g of NH4NO3 and 1.1g of KNO3. The third one consists of 5.2g of LiNO3, 13.7g of NH4NO3 and 1g of NH4Cl) and the fourth one consists of 1.77g of LiNO3, 2.94g of NH4NO3, 1g of NaNO3 and 1g of NaCl. The latent heat and the melting point of the respective salt and their eutectic mixture were determined using digital differential scanning Apparatus. The results obtained showed that the melting points and latent heats of the first, second, third and fourth eutectic mixture were 79.50C and 112kJ/kg, 80.50C and 114kJ/kg, 81.40C and 109kJ/kg, 84.40C and 119kJ/kg respectively. In view of this, the eutectic mixture of 1.77g of LiNO3, 2.94g of NH4NO3, 1g of NaNO3 and 1g of NaCl with melting point of 84.40C and latent heat of 119KJ/Kg was found to possess the best thermal energy storage capability compared to others..Keywords—Eutectic mixture, Salts, Phase change materials (PCM), Latent heat storage

Improving the thermal energy storage capability of diatom-based biomass/polyethylene glycol composites phase change materials by artificial culture methods

We report a novel shape-stabilized phase change materials (SSPCMs) made from polyethylene glycol (PEG) and diatom-based biomass. The diatom materials were prepared by artificial culture and simple acid pickling and sintering. Scanning electron microscope (SEM), Fourier transform infrared spectroscopy (FT-IR), X-ray diffractometry (XRD) and polarizing microscopy (POM) were used to characterize the prepared materials, such as their chemical composition, morphology, crystallization performance and so on. The results indicated that no chemical reaction occurred between PEG and diatom-based biomass during the preparation process, but the crystalline regions of PEG were decreased. Differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and thermal cycling tests showed that the SSPCMs with sintered diatom frustules as the supporting material have a good phase change performance and thermal stability in the PEG solid-liquid phase transition region. The maximum latent heat values in the melting and crystallization processes are around 121.54 J/g and 127.20 J/g respectively, and the relative enthalpy efficiency reaches up to ~98.1%. At the same time, the prepared SSPCMs have reliable heat storage and temperature-regulated performance. Our study demonstrates the great potential and significance for the practical application of artificially cultured diatom-based biomass in phase change materials for waste heat recovery and temperature regulation.

Liquid Thermo-Responsive Smart Window Derived from Hydrogel

Summary Buildings account for 40% of global energy consumption, while windows are the least energy-efficient part of buildings. Conventional smart windows only regulate solar transmission. For the first time, we developed high thermal energy storage thermo-responsive smart window (HTEST smart window) by trapping the hydrogel-derived liquid within glasses. The excellent thermo-responsive optical property (90% of luminous transmittance and 68.1% solar modulation) together with outstanding specific heat capacity of liquid gives the HTEST smart window excellent energy conservation performance. Simulations suggested that HTEST window can cut off 44.6% heating, ventilation, and air-conditioning (HVAC) energy consumption compared with the normal glass in Singapore. In outdoor demonstrations, the HTEST smart window showed promising energy-saving performance in summer daytime. Compared with conventional energy-saving glasses, which need expensive equipment, the thermo-responsive liquid-trapped structure offers a disruptive strategy of easy fabrication, good uniformity, and scalability, together with soundproof functionality that opens an avenue for energy-saving buildings and greenhouses.

Thermal transport properties enhancement of paraffin via encapsulation into boron nitride nanotube: a molecular dynamics study

This research investigates a novel composite of encapsulated paraffin in boron nitride nanotube (BNNT) which is more thermally and chemically stable than carbon nanotube. This composite can achieve high thermal conductivity and, meanwhile, have thermal energy storage capability for efficient thermal management under extreme conditions. Equilibrium molecular dynamics simulations were conducted to study self-diffusion coefficient, thermal conductivity, and specific heat of encapsulated paraffin. The simulation results indicated that the self-diffusion coefficient and thermal conductivity of paraffin could be increased by up to 10 and 7 times, respectively, while specific heat was reduced after encapsulating into BNNT.

Development of eco-sustainable plasters with thermal energy storage capability

In order to limit the energy demand of buildings, a possible strategy consists in the storage of thermal energy using phase change materials (PCMs). In this work, an innovative PCM-enhanced plaster, fully formulated by using materials coming from natural resources, was developed. The PCM (i.e., a biodegradable material from agricultural resources having a melting temperature of 23 °C) was shape-stabilized with a direct absorption method by using a proper combination of different inorganic powders, taking into account also the final cost of the product and the processability issues. The most important physical properties of the plaster were then investigated following the European standards and compared with those of a natural hydraulic lime commercial plaster. The optimized PCM-enhanced plaster could be classified as a lightweight plaster (LW class according to UNI EN 1015-10) with compressive strength CSI (UNI EN 1015-11) and water absorption class W2 (UNI EN 1015-18). Differential scanning calorimetry tests confirmed the thermal energy storage capability of the PCM-enhanced plaster, even though plaster processing operations slightly decreased the specific melting enthalpy of the PCM within the plaster. Moreover, small-scale simulations were performed through the monitoring of the inner temperature of an insulated box, in which a plaster layer was applied on the internal walls, during heating and cooling ramps. These tests confirmed the thermal energy storage capability of the newly developed plaster around the PCM melting temperature interval.

MXene-wrapped bio-based pomelo peel foam/polyethylene glycol composite phase change material with enhanced light-to-thermal conversion efficiency, thermal energy storage capability and thermal conductivity

Phase change materials (PCMs) have attracted great interest from researchers and have been widely developed in the field of solar thermal energy storage. Herein, a novel bio-based pomelo peel foam (PPF)/polyethylene glycol (PEG) composite PCM was designed and prepared via the simple impregnation process, which is further modified with low loading of MXene nanosheets for the purpose of improving its light-to-thermal conversion efficiency, thermal energy storage capability and thermal conductivity. With the incorporation of MXene nanosheets into PPF, the light-to-thermal conversion efficiency was improved obviously, the loading of PEG in form-stable composites phase change materials (FCPCMs) increased from 86.9 wt% (FCPCM-1) to 96.2 wt% (FCPCM-2, FCPCM-3 and FCPCM-4), and the thermal conductivity of obtained PPF@MXene/PEG FCPCMs was also improved (from 0.25 W/mK to 0.42 W/mK). It shows that the obtained PPF@MXene/PEG FCPCMs can be fully utilized in the field of solar thermal energy storage.