Composite Thermal Energy Storage Research Articles

In-Situ Reaction Method to Synthetize Constant Solid-State Composites as Phase Change Materials for Thermal Energy Storage.

The encapsulation and heat conduction of molten salt are very important for its application in heat storage systems. The general practice is to solidify molten salt with ceramic substrate and enhance heat conduction with carbon materials, but the cycle stability is not ideal. For this reason, it is of practical significance to study heat storage materials with a carbon-free thermal conductive adsorption framework. In this paper, the in-situ reaction method was employed to synthetize the constant solid-state composites for high-temperature thermal energy storage. AlN is hydrolyzed and calcined to form h-Al2O3 with a mesoporous structure to prevent the leakage of molten eutectic salt at high temperature. Its excellent thermal conductivity simultaneously improves the thermal conductivity of the composites. It is found that 15CPCMs prepared with 15% water addition have the best thermal conductivity (4.928 W/m·K) and mechanical strength (30.2 MPa). The enthalpy and the thermal storage density of 15CPCMs are 201.4 J/g and 1113.6 J/g, respectively. Due to the excellent leak-proof ability and lack of carbon materials, the 15CPCMs can maintain almost no mass loss after 50 cycles. These results indicate that 15CPCMs have promising prospects in thermal storage applications.

Development and characterization of NaCl-KCl/Kaolin composites for thermal energy storage

Molten chloride salts are considered a promising thermal storage materials because of their high energy storage density and thermal stability. However, the application of molten chloride salts is districted by its the corrosion behavior with metal containers. Encapsulation is one viable method for corrosion prevention. In this study, molten chloride salts as phase change materials (PCMs) were combined with encapsulation materials to form stable shape phase change materials (SSPCMs). The PCM was the mixture of NaCl and KCl eutectic salts, and the encapsulation material was kaolin. The SSPCMs were prepared by direct mixing and sintering, and the morphology and the thermal behaviors of the SSPCMs were investigated. The results showed that PCMs were uniformly distributed in kaolin, and the kaolin was compatible with NaCl-KCl. With the increase of the ratio of NaCl-KCl eutectic salt, the latent heat and energy storage density of SSPCMs increased. Meanwhile, the results indicated that the NaCl-KCl/kaolin composite with salt content of 80 wt% demonstrated the best performance with the phase change enthalpy of 178 J/g and the energy storage density of 171.32 J/cm3. Besides, it could maintain intact shape after 400 thermal cycling tests from 600 to 700 °C.

Experimental study on novel phase change composites for thermal energy storage

Experimental study on novel phase change composites for thermal energy storage

Thermal conductivity enhancement and shape stabilization of phase change thermal storage material reinforced by combustion synthesized porous Al2O3

The utilization of paraffin in latent heat storage system is limited by its leakage and low thermal conductivity. To address such challenges, we prepare composite phase change materials (PCMs) with enhanced thermal conductivity and shape stability. Paraffin is supported by porous Al2O3 which is synthesized by solution combustion synthesis (SCS). The porous structure of Al2O3 is quite influenced by the fuel species in SCS reactions. The glycine-induced Al2O3 shows highly hierarchical porous structure, which can improve the anti-leakage performance of the composites. The thermal conductivity of Al2O3/PW reaches 1.27 W/m•K with an Al2O3 mass ratio of 50 wt%, which is 5 times of pure paraffin. The composite also presents acceptable latent heat capacity of higher than 100 J/g and very good thermal cycling stability. These characteristics assure the promising application of Al2O3/PW composites for thermal energy storage.

Combined effects of composite thermal energy storage and magnetic field to enhance productivity in solar desalination

The conventional solar still is limited to a daily yield of approximately 2–3.5 kg/m2/day. To increase the yield, this study investigates experimentally the combined effects of latent and sensible energy storage together with magnetization. Paraffin and novel high-thermal conductivity nanomaterial (graphite plate) were used as latent and sensible heat storage materials, respectively. There was an overall increase of 62% and 235% in the daytime and night-time yield, respectively, giving a total yield of 5.5 kg/m2/day compared to 3.4 kg/m2/day for a conventional still. Enviro-economic parameters like emissions, CO2 mitigation and carbon credit (CC) earned were also investigated. Energy matrices analysis and water quality checks were performed to estimate the energy-payback time, life cycle conversion efficiency (LCCE) and purity of desalinated water. The cost per liter of freshwater was found to be 3.7% cheaper than for a conventional still and 69% cheaper than bottled water in India. Over a 30 year period, 40.3 Tonnes of CO2 will be mitigated contributing a CC and LCCE of $402 and 0.52, respectively. The proposed modified still is recommended as a substitute for conventional stills and stills with simple energy storage.

Development and Characterization of Concrete/PCM/Diatomite Composites for Thermal Energy Storage in CSP/CST Applications

Thermal energy storage (TES) systems for concentrated solar power plants are essential for the convenience of renewable energy sources in terms of energy dispatchability, economical aspects and their larger use. TES systems based on the use of concrete have been demonstrated to possess good heat exchange characteristics, wide availability of the heat storage medium and low cost. Therefore, the purpose of this work was the development and characterization of a new concrete-based heat storage material containing a concrete mix capable of operating at medium–high temperatures with improved performance. In this work, a small amount of shape-stabilized phase change material (PCM) was included, thus developing a new material capable of storing energy both as sensible and latent heat. This material was therefore characterized thermally and mechanically and showed increased thermal properties such as stored energy density (up to +7%, with a temperature difference of 100 °C at an average operating temperature of 250 °C) when 5 wt% of PCM was added. By taking advantage of these characteristics, particularly the higher energy density, thermal energy storage systems that are more compact and economically feasible can be built to operate within a temperature range of approximately 150–350 °C with a reduction, compared to a concrete-only based thermal energy storage system, of approximately 7% for the required volume and cost.

Biogenic architectures for green, cheap, and efficient thermal energy storage and management

A key challenge for efficient thermal management of civil buildings is the development of shape-stabilized phase change materials (PCM) for thermal energy storage and release. Nevertheless, some issues related to the disposal of such devices are arising as they are generally not biodegradable and recyclable. In this work, we developed two new renewable and biodegradable thermal energy storage composites obtained from renewable resources. These are based on the use of bio-derived alcohol as PCM and on porous biogenic structures, namely cuttlebone and pomelo peel, as shape stabilizers, which are currently waste materials. The results point out that both cuttlebone and pomelo peel can spontaneously absorb huge amounts of the considered PCM and retain it in the liquid state. The thermal energy storage capacity of the composites is about 70% that of neat PCM, whereas the volumetric efficiency (i.e., the ratio between the thermal energy storage capacity of the composite and the neat PCM in J cm−3) approaches 90% and 70% in cuttlebone and pomelo peel composites, respectively. The properties appear stable over at least 100 melting/solidification cycles.

Using triply periodic minimal surfaces (TPMS)-based metal foams structures as skeleton for metal-foam-PCM composites for thermal energy storage and energy management applications

Organic phase change materials (PCMs), such as paraffin wax, have shown great potential for their utilization in latent heat thermal energy storage systems (LHTES). However, due to their low thermal conductivity, they are often hybridized with high thermal conductivity metal foam, resulting in metal foam-PCM composites (MFPCMs) with enhanced heat transfer features. Conventional metal foam is usually idealized using the Kelvin cell. Owing to the recent advances in 3D printing, any complicated topology can however be easily manufactured, which paves a pathway for other complex cell types to be utilized in such energy systems other than Kelvin cell. In this exploratory work, three Triply Periodic Minimal Surfaces (TPMS), i.e., Gyroid, I-graph and wrapped package-graph (IWP), and Primitive cells, are (to the best of the knowledge of the present authors), used for the first time, as skeleton for MFPCMs composites to enhance the effective thermal conductivity of conventional PCMs. Transient numerical simulations were performed to compare the thermal energy storage performance of the used TPMS-based PCM composites with their counterpart based on the conventional Kelvin cell. All structures were tested at the same porosity level and unit cell size of 90% and 7 mm, respectively. Simulations were done under two boundary conditions namely isothermal and isoheat flux conditions. Steady state simulations were also performed to assess the effective thermal conductivity of the used MFPCM composites at temperatures below the melting temperature of used PCM (pure conduction). The obtained results stress that the effective thermal conductivity of MFPCMs strongly depends on the cell type and its unique architecture and not only on the cell porosity where significant increase in the effective thermal conductivity of the MFPCMs composites was achieved when the three TPMS structures are used. Under isothermal condition while considering the Kelvin-based MFPCM as the baseline case, the PCM melting time was reduced by approximately 31% for the Gyroid, 40.3% for the IWP, and 35.3% for the Primitive-based MFPCMs. In isoflux case, the PCM melting time did not show dependence on the type of metal foam structure. However, by considering the temperature homogeneity as a performance indicator (quantified by the maximum and minimum temperature difference in PCM domain), Kelvin-based MFPCM showed the highest value for the difference (least homogenous) whereas, IWP-based MFPCM on average was almost 5 K lesser than the Kelvin-based MFPCM during the entire melting process. Therefore, TPMS structures showed superior performance than the Kelvin cell, let alone than the case of PCM alone, which makes them promising candidates for potential utilization in LHTES applications.

A novel composite for thermal energy storage from alumina hollow sphere/paraffin and alkali-activated slag

This study proposes a novel thermal energy storage composite (TESC) with an alumina ceramic-based form-stable phase change material (FSPCM) as the phase-change aggregate and alkali-activated slag as the matrix material. FSPCM was prepared with alumina hollow sphere as the supporting material and paraffin as the phase change material (PCM). A series of tests were conducted to investigate the thermo-mechanical properties of the TESC. The results show that the phase transition peak temperature of FSPCM is 23.6 °C, the latent heat value is 69.8 J/g, and the paraffin adsorption mass fraction with respect to the alumina hollow sphere can be as high as 82.33%. As the mass fraction of FSPCM increases from 0% to 80%, the latent heat value increases from 0 J/g to 19.18 J/g, while the compressive strength can still be maintained above 24.04 MPa. The effective thermal penetration depth and the thermal energy storage performance of the TESC were mathematically analysed and experimentally tested. Meanwhile, the influence of FSPCM dosage on the mechanical strength of the TESC and the microstructure characteristics of the interface transition zone between FSPCM and the matrix were investigated. A mathematical model with a maximum relative error of 12.08% was established for predicting the 28-day compressive strength of TESC.

Novel and durable composite phase change thermal energy storage materials with controllable melting temperature

The development of high temperature phase change materials (PCMs) with great comprehensive performance is significant in the future thermal energy storage system. In this study, novel and durable Al-Si/Al2O3-AlN composite PCMs with controllable melting temperature were successfully synthesized by using pristine Al powder as raw material and tetraethyl orthosilicate as SiO2 source. The Al2O3 shell and Al-Si alloy were in-situ produced via the substitution reaction between molten Al and SiO2. Importantly, the crack caused by the incomplete encapsulation of the Al2O3 shell could repair itself by the nitridation reaction of internal molten Al and thereby forming a highly dense Al2O3-AlN composite shell. The produced dense Al2O3-AlN composite shell could significantly improve the thermal cycling stability of composite PCMs, and thus, the thermal storage density decrease of the Al-Si/Al2O3-AlN (59.8 J/g to 77.7 J/g) was far less than that of the Al-Si/Al2O3 (118.5 J/g) after 3000 thermal cycles. Moreover, the synthesized Al-Si/Al2O3-AlN still exhibited a controllable melting temperature (571.5–637.9 ℃), relatively high thermal storage density (105.6–150.7 J/g), great dimensional stability and structural stability after 3000 thermal cycles. Hence, the synthesized Al-Si/Al2O3-AlN composite PCMs, as promising preferential thermal energy storage materials, can be stably used in the energy utilization efficiency improvement of various systems for more than 6 years.

Red mud-molten salt composites for medium-high temperature thermal energy storage and waste heat recovery applications

Red mud (RM) is an industrial waste of the aluminum industry with presently estimated worldwide legacy-site stockpiles of 4 billion tones. RM is typically disposed in the sea, dams or dykes, posing a significant environmental hazard due to its high alkalinity and traces of heavy metals. Despite recent valorization efforts, only 15% of RM deposits are currently utilized. In this work, a novel use of RM to formulate composite phase change materials (CPCMs) is proposed. The CPCM is formulated by milling nitrate salts with RM, compressing and subsequent sintering of the two. Overall good performance over the temperature range of 25–400 ℃ is observed. Maximum latent heat of the CPCMs is 58 J/g, while average thermal conductivity and Cp are in the range of 0.77–0.83 W/mK and 1.03–1.31 J/g ℃, respectively. No variations in the melting point or latent heat are observed after 48 cycles. Energy storage density is calculated to be up to 1396 MJ/m3. The working temperature of this novel CPCM make it ideal for waste heat recovery of medium-high temperature waste heat streams providing a valorization pathway and valorization for RM as a by-product for energy-related applications.

The design of phase change materials with carbon aerogel composites for multi-responsive thermal energy capture and storage

Fe-doped carbon aerogel-based composite phase change materials exhibit the ability to respond to light, electricity, and magnetism as well as temperature for multi-responsive thermal energy capture and storage.

Evaluating the thermal efficiency of microencapsulated phase change materials for thermal energy storage in cementitious composites

Microencapsulated phase change materials (MCPM) have been shown to be a promising material that can be used in cementitious composites for thermal energy storage. This paper evaluates the thermal efficiency of MPCM incorporated in the cementitious composite and quantitatively identifies the influential mechanical and chemical damages that can lead to reductions in thermal efficiency of MPCM with melamine formaldehyde based shell. Longitudinal Guarded Comparative Calorimetry (LGCC) and Low Temperature Differential Scanning Calorimetry (LT-DSC) were used to quantitatively evaluate the thermal response of cementitious composite containing MPCM, in relatively large (10−2 m) and small (10−3 m) scale samples, respectively. The results indicated an average reduction of ~32%–34% in the effective thermal efficiency (i.e., the average ratio of measured over expected heat release/absorption) of cementitious composite containing MPCM due to mechanical as well as chemical damages to MPCM. Mixing speeds of various rate was also studied and it was found that sample preparation at slow mixing speed (i.e., 55 rpm) could cause minimal damage to the MPCM (i.e., ~5.5 %-7.5% reduction in thermal efficiency), while using fast mixing speed (i.e., 165 rpm) can reduce the thermal efficiency of MPCM by up to 50%. Exposure of plain MPCM to separate constitutes of synthesized pore solution indicated that the main cause of MPCM thermal efficiency reduction is its chemical reaction with the pore solution of the cementitious composite. It was found that the main constitute of pore solution that could chemically interacts with MPCM was SO42-. Finally, it was observed that the incorporation of MPCM in the cementitious composite can reduce the compressive strength of mortars due to the soft nature of MPCM. To increase the thermal efficiency of MPCM, this work recommends potential solutions such as using a cement with low sulfate content or development of a shell material for MPCM which is unreactive when exposed to pore solution.

Design and Optimization of Lamellar Phase Change Composites for Thermal Energy Storage

Phase change materials offer thermal energy storage (TES) and are often integrated with high conductivity materials to increase power density. However, the design and optimization of such composites are historically based on intuition, as the computational techniques used to predict behavior in these systems are generally too expensive to perform parametric studies. Herein, a general design framework is developed and demonstrated that is optimized for TES in parallel lamellar structures, to identify the critical pitch required to treat the composite as a single effective medium and the optimum volume fraction of high conductivity material in the lamellar composite. The optimization criteria is tested experimentally using 3D printed AlSi12 alloy and octadecane. The composite system exhibits a critical pitch between a lamella of 1 mm and the optimum volume fraction for the high conductivity material is 0.6–0.8. The design principles demonstrated here show that the size and volumes of conductive materials are much larger than the current state of the art, and this framework provides a holistic approach to design for such future materials for TES applications.

Designing of latent heat thermal energy storage systems using metal porous structures for storing solar energy

The present work consists of increasing the thermal conductivity of the phase change materials (PCM) using metal foam structures for storing solar energy in form of thermal heat. In this regard, copper foam and copper/aluminium wire woven foam structures have been used to increase the thermal conductivity for a faster heat storage and extraction of heat from the PCM. The latent heat thermal energy storage (LHTES) systems with capacity of storing 300 KJ of thermal energy have been designed using the PCM and metal foam structures. Both the PCM–aluminium wire woven foam and PCM-copper foam composites took similar time for melting of PCM. The heat extraction of PCM–aluminium wire woven foam was high and found to be comparable to the PCM–copper foam composite system. The thermal efficiency of the various PCM-foam composite thermal energy storage tanks ranged from 60–70 % and 80–85 % on using water and air as the heat extraction media. The heat extraction continued for 3 – 4 hrs in case of cold water and 7 – 8 hrs in the case of cold air. The temperature of the cold air/water increased to 2 – 2.5 times of the original temperature after passing through the LHTES.

The performances of expanded graphite on the phase change materials composites for thermal energy storage

For the storage of latent thermal energy (LTES), phase change materials (PCM) are the most commonly used. Nonetheless, their low thermal conductivity values and the liquid leakage on the transition phase of process limits their application. Hence, the stabilization-form can be a solution to surmount these two limitations. In this work, the Hexadecane with large latent heat was used as PCM, styrene-b-(ethylene-co-butylene)-b-styrene (SEBS) tri-block copolymer and the low-density polyethylene (LDPE) served as the supporting materials and expanded graphite (EG) was added for improving the thermal conductivity. We focused on the preparation of SEBS/Hexadecane/LDPE Composites and the improvement of the heat transfer using the EG. The Fourier Transformation Infrared spectroscope also demonstrated a good compatibility between SEBS, LDPE, Hexadecane, and EG. The transient Guarded Hot Plate Technique (TGHPT) and a Thermogravimetric analyzer were utilized to assess the thermal properties and thermal stability of the PCM composites respectively. Further, a leakage test proved that the composite has an excellent form-stable property. Thanks to expanded graphite, no hexadecane leakage was depicted at a 75% mass fraction of PCM in composites, which surmounts almost all mass fraction values reported in the literature.

Thermophysical Properties Characterization of Sulphoaluminate Cement Mortars Incorporating Phase Change Material for Thermal Energy Storage

Efficient use of solar energy by thermal energy storage composites and utilizing environmentally friendly cementitious materials are important trends for sustainable building composite materials. In this study, a paraffin/low density polyethylene (LDPE) composite shape-stabilized phase change material (SSPCM) was prepared and incorporated into a sulphoaluminate cement (SAC) mortar to prepare thermal energy storage mortar. The thermal and mechanical properties of SSPCM and a SAC-based thermal energy storage material (SCTESM) were investigated. The result of differential scanning calorimeter (DSC) analysis indicates that the latent heat of SCTESM is as high as 99.99 J/g. Thermogravimetric analysis demonstrates that the SCTESM does not show significant decomposition below 145 °C. The volume stability test shows the volume shrinkage percentage of the SCTESM is less than that of pure SAC mortar and far less than that of ordinary Portland cement mortar. The SCTESM has high early strength so that the compressive strength at 1-, 3-, and 7-day curing age is up to that at 28-day curing age of 67.5%, 78.3%, and 86.7%, respectively. Furthermore, a mathematical prediction model of the SCTESM compressive strength was proposed. The investigation of latent heat storage characteristics and the thermoregulating performance reveals that SCTESMs have the excellent capacity of heat storage and thermoregulating.

Effect of convection on melting characteristics of phase change material-metal foam composite thermal energy storage system

Abstract A pore-scale numerical model is presented for simulating the melting of phase change material (PCM) in a PCM-metal foam composite energy storage system. Instead of considering volume averaged domain for simulating the melting process, the present model resolves the geometry of the metal foam. Thus it can capture the effects of geometrical parameters such as the pore size and pore distribution as well as the localized heat transfer at the metal foam PCM interface more accurately. The model also incorporates the effect of convection on the melting process. The developed model comprises of a geometry creation model for generating the foam structure considering metal foam as overlapping circular pores of different pore radius. Heat transfer, phase change and convection are solved using an enthalpy based finite volume model. The model is validated with experimental results given in literature. Subsequently, the effect of convection on melting and energy storage rate in PCM-metal foam composite systems is studied for different pore size and different porosity of metal foam. Results indicate that the effect of convection is higher for higher porosity and larger pore size.

Overall evaluation of single- and multi-halide composites for multi-mode thermal-energy storage

Sorption thermal-energy storage plays a critical role in addressing the mismatch between thermal-energy consumption and supply. However, the previous evaluations of sorption thermal-energy storage materials and cycles were mainly based on the equilibrium results of energy storage density. In this study, we develop evaluation models to provide an optimal working pair selection reference for single-stage sorption/resorption cycles under short- and long-term storage modes, and compare the thermal-energy storage density in the discharging stage, the effective discharging time, the temperature gradient, the exergy output during the discharge phase (ΔEdis), and the exergetic coefficient of performance (ECOP). By considering ΔEdis as a criterion, the best halides are determined to be NH4Cl and CaCl2 for single-stage sorption cycles at heat-source temperatures of 60–80 °C and 90–180 °C, respectively; however multi-halide can be a better choice when the temperature varies over optimal temperature range of single-halide, i.e., from 80 °C to 160 °C. Resorption is also analysed in this study. The results show that multi-halide is not suitable for resorption cycles because a part of the components will fail to sorb during the discharging stage. The effective reaction-temperature ranges of the resorption cycles are wider than those of the corresponding sorption cycles, whereas the performance values decrease mainly because of the larger required sorbent mass.

New prominent lithium bromide-based composites for thermal energy storage

Abstract Four different LiBr-based composite materials have been synthesized with silica gel or activated carbon as host porous matrix. High salt contents were incorporated in these composites: 37 wt% and 53 wt% for silica gel/LiBr composites; 32 wt% and 42 wt% for activated carbon/LiBr composites. The performance of these materials in conditions representative of the applications of sanitary hot water production and space heating demonstrates the very high potential of the silica gel/LiBr 53 wt% composite. It exhibits an unprecedented energy storage density of 261 kWh/m3 (adsorption temperature: 30 °C, desorption temperature: 80 °C and water vapor pressure of 12.5 mbar) and of 381 kWh/m3 when the desorption temperature reaches 120 °C. This promising material presents a good composition homogeneity, high water uptakes between 10 °C and 80 °C, and no measurable loss of sorption properties upon 10 cycles. This composite was tested in an open type laboratory set-up to complete its analysis for heat storage applications, at the scale of 200 g. The best energy storage density reached during 3 h 26 min was as high as 246 kWh/m³ (adsorption temperature: ~29 °C and water vapor pressure of ~12.5 mbar).