High Temperature Phase Change Materials Research Articles

Research on the Thermal Insulation Performance of High Temperature Gradient Composite Insulation Material

In this study, the high temperature gradient composite insulation material (SGIM) was prepared by using zirconia fiber and carbon fiber (CZ), high temperature phase-change material (HPCM), microcellular thermal insulation material of calcium silicateas (CS/AS), insulation material of nano-silica(NP) and radiation shielding material as raw materials. The thermal insulation performance was simulated by using the finite element software. The heat insulation performance of the material was tested by oxy-acetylene ablation experiment. The thickness of the insulation material was also set to 32 mm. The temperature of hot surface was controlled at 2000°C. After 600 seconds, the material of cold temperature was 54°C. The excellent performance of SGIM insulation is demonstrated.

Experimental validation of high-temperature latent heat storage model using melting front propagation data

Renewed interest in concentrated solar power has sparked increase in research concerning high temperature phase change materials. A large number of these studies are focused on numerical modeling and heat transfer optimization. However, most of these models are validated using either inadequate (low temperature) experimental data for low-temperature melting or temperature measurements acquired during melting in very specific geometries. The goal of this paper is to help fill the gap in the available experimental data for model validation by providing unique directly measured front propagation data for high temperature phase change materials.The experimental setup for direct melting front propagation acquisition during the sodium nitrate melting is presented. Three experiments with different Rayleigh numbers and orientation are presented. The acquired data was used for numerical model validation. The model was based on the finite volume approach using the frequently used enthalpy-porosity method. It is shown that the best results are obtained using much larger values of the mushy zone constant than those found in literature. Furthermore, by comparing temperature profiles between the experiment and simulations it is shown that temperature measurements (which are one of the most used validation methods) can, in some cases, lead to a false validation.

A novel multiwalled LiF@GO@SiO2 microcapsule with high phase change temperature

High temperature phase change materials (PCMs)-encapsulated microcapsules with large heat exchange area for addressing specific energy storage have increasing application potentials in many fields. Herein, a novel hybrid multiwalled microcapsule LiF@GO@SiO2 with high phase change temperature was designed and fabricated, which could overcome strong corrosion and volume expansion of lithium fluoride (LiF) during heat storage process. The multiwalled structure of microcapsule contained three layers, consisting of volume expansion buffer layer polydopamine (PDA), anti-corrosion leakage-proof layer (GO) and heat-resist strength layer (SiO2), respectively. Volume expansion buffer layer would be vanished during thermal cycling, and GO as well as SiO2 layers played important roles in protecting molten LiF from leakage. A series of tests including SEM, SEM-EDS, FTIR, XPS, XRD and TGA revealed that three-layer shells were sequentially coated on the surface of core material LiF successfully. Besides, DSC results via quantitatively analyzing, indicated that LiF@GO@SiO2 microcapsules had high phase change temperature of 848 °C, encapsulation ratio of 82.0% and latent melting heat of 894.5 J/g. In addition, encapsulation ratio of the microcapsule had a minor deflection within 5% after 10 times loops by calculating and comparing corresponding enthalpies, which displayed prepared microcapsule could be used repeatedly in high temperature energy storage. Overall, our results opened new avenues for the utilization of high temperature PCMs and their packaging technique.

A strategy for designing microencapsulated composite phase change thermal storage materials with tunable melting temperature

Thermal energy storage technology with high temperature phase change materials (PCMs) plays an increasingly important role in the concentrated solar power plants and industrial waste heat recovery systems. In this study, a novel displacement reaction between tetraethoxysilane as SiO2 source and molten raw Al powder was purposed to successfully prepare Al-Si/Al2O3 high temperature composite PCMs. Interestingly, by proposed synthetic methodology, we not only achieved the in-situ synthesis of Al-Si alloy PCM and Al2O3 shell, but also realized the controllability of Al-Si alloy composition and Al2O3 shell layer thickness. Our results indicated that the melting temperature of the prepared composite PCMs depended on the composition of Al-Si alloy, and could be designed within a certain temperature range (from 574.0 °C to 641.4 °C), instead of a particular temperature point. The melting temperature adjustability of the prepared composite PCMs provided an additional flexibility in different working temperature conditions. Moreover, the prepared composite PCMs exhibited a relatively high thermal storage capacity (248.6 J/g to 331.0 J/g), good thermal stability, excellent repeatable utilization property and certain shell layer self-repairing ability in the working temperature range. Therefore, the prepared composite PCMs can prove to be promising thermal energy storage materials for improving the energy efficiency in various systems under different working temperature conditions.

Review on the development of high temperature phase change material composites for solar thermal energy storage

The development of cost-effective and reliable high temperature phase change materials (HTPCMs) for solar thermal energy storage is an important step in the future application of concentrated solar thermal technologies. Inorganic eutectic salts relying on their advantages such as low cost, high melting temperatures and latent heats of fusion, are promising candidates for HTPCMs. However, both the thermal conductivity and thermal stability of the inorganic salts are relatively low. In addition, they have corrosion issues with containment materials at high temperatures. All of these issues have been problematic for their use in this application. A potential solution to these issues is the development of HTPCM composites, where high temperature molten salts as PCMs are encapsulated by supporting materials to achieve improved corrosion resistance with containment materials and enhanced thermal conductivity and thermal stability. This paper reviews current trends and recent developments in the preparation and classification of high temperature (>300 °C) PCM composites. The effect of developed HTPCM composites on their melting point, latent heat of fusion, thermal stability and heat transfer performance are also discussed in the context of this review.

Linear parabolic trough solar power plant assisted with latent thermal energy storage system: A dynamic simulation

One of the efficient solar energy harvesting technics is the parabolic trough concentrated solar power plant. However, if the concentrated solar power plant were not equipped with a storage system, the power plant capacity factor would be deficient. Latent thermal energy storage system using phase change material (PCM) is a high energy density storage system to provide durable energy with a constant temperature. In this study, first, a dynamic analysis is performed implementing TRNSYS software on the parabolic trough concentrated solar power plant located in Shiraz, Iran. Consequently, this system is assisted by the latent thermal energy storage system to improve its performance and capacity factor. Several high-temperature PCMs, namely H250, NaNO3, KNO3, and KOH, are examined in the latent thermal energy storage system. The simulation depicts that owing to the operational condition of Rankin cycle in this study, using NaNO3 in the latent thermal energy storage system is the best option with a higher solar fraction (34.14%) among other examined PCMs. In this case, the solar fraction has been enhanced by 90.5% in comparison with the solar power plant without the latent thermal energy storage system. The economic analysis illustrates that the payback period, IRR and NPV of the added LTES system are obtained as 11 years, 15.6% and, 617825$, respectively. The result of the sensitivity analysis on NPV revealed that the electricity price has the most effect on NPV and enhancing the electricity price has a positive impact on NPV.

Characterisation of promising phase change materials for high temperature thermal energy storage

Abstract In the current study two phase change materials have been initially characterised as potential high temperature phase change materials (PCM) for thermal energy storage. Thermophysical properties such as melting/freezing point, latent heat, and specific heat capacity were determined using differential scanning calorimetry (DSC). Results from the uncycled PCMs show a melting point of 541.98 ± 0.15 °C and a latent heat of 164.96 ± 3.83 J/g for the lower temperature PCM (BaCl2-KCl-NaCl), and 706.92 ± 0.34 °C and 133.14 ± 3.55 J/g for the higher temperature PCM (K2CO3-Na2CO3). This largely compares well with the melting points and latent heats provided in literature. Theoretical predictions of other properties such as solid and liquid density, liquid thermal conductivity, and viscosity were also estimated. Lastly, samples of the PCM were also cycled up to 200 times with the melting point and latent heat measured. From the cycling results, the melting point and latent heat of samples cycled 200 times show almost no change. The measured melting point and latent heat after 200 cycles was found to be 541.30 ± 0.16 °C and 161.64 ± 2.60 J/g, respectively, for the low temperature PCM. Similarly, the higher temperature PCM showed good cycling stability after 200 cycles with a melting point and latent heat of 704.62 ± 0.29 °C and 135.42 ± 3.59 J/g, respectively. Overall, it was found that the PCMs investigated in the current study show promising results to be considered as high temperature energy storage materials.

Design optimization of the phase change material integrated solar receiver: A numerical parametric study

Dish-Micro Gas Turbine (D-MGT) systems can be an effective way of power production (<100 kW) in rural areas having limited access to electricity. In such no fuel assisted systems, the stability of the input thermal power to the MGT is an important concern as MGT is sensitive to the temperature variations caused by the natural fluctuation of the solar flux. To reduce this effect, a novel solar receiver has been proposed integrated with a Phase Change Material (PCM) for the short-term thermal energy storage. The proposed receiver is cylindrical shaped filled with PCM, with a conical cavity on the front surface and heat transfer fluid tubes immersed in the PCM. This paper deals with the investigation of the optimum design point of the proposed receiver based on the required input parameters of the MGT. The numerical simulations have been conducted using Computational Fluid Dynamic methods to pre-evaluate the effect of many controlling parameters on the temperature, PCM liquid fraction, pressure loss and outlet thermal power of the receiver. Surface-to-Surface (S2S) radiation model has been employed along with the ray-tracing model for the constant concentrated solar flux of 500 kW/m2 on the receiver aperture surface. The influencing factors considered in this study include the high-temperature PCMs, receiver cavity dimensions, incident solar flux, hot wall thickness, tube diameter and the number of the tubes, pressure drop inside the tubes and the inlet mass flow rate. Results demonstrate the considerable effect of each variable on the receiver output parameters, and this leads to the identification of optimum design point. The result of the study offers valuable guidelines for the receiver development for further experimentation.

Numerical Study on Enhancement of Heat pipe-nickel foam to High Temperature Phase Change Thermal Storage

High temperature phase change thermal energy storage could be widely applied in the fields of solar power systems, industrial waste heat recovery, etc., while the drawback of low thermal conductivity constrains the application of phase change thermal energy storage. The enthalpy-porosity technique was employed to analyze the performance of a thermal energy storage unit with square container and high melting temperature phase change material enhanced by heat pipes and nickel foam. The melting performance of the phase change material with different thermal enhancement methods has been studied. The obtained results reveals that heat pipe is more effective than the nickel foam, and the heat pipe-nickel foam mode could effectively shorten the melting process and decrease the temperature difference within the phase change material in the container. The simulation could provide a significant reference to the phase change energy storage system enhanced by heat pipes.

Assessment of Heat Transfer Characteristics of a Latent Heat Thermal Energy Storage System: Multi Tube Design

In this study, a numerical investigation of heat and mass transfer characteristics of a high temperature phase change material (PCM) is presented. The phase change material used is Sodium Nitrate with a melting point of 306 °C. For a fixed PCM mass, investigations are carried out on a multi-tube heat exchanger system for examining the effects of tube size and number of tubes on overall heat transfer rate. The performance of latent heat storage system during the charging and discharging processes are discussed. Further, the results are elaborated for three multi-tube systems to optimize the number of tubes to be used with the constant heat transfer surface area. The natural convection pattern during charging is observed with the help of temperature contours and streamlines. The solidification front pattern of the PCM, during the discharging process is visualized through melt fraction contours. With the increase in the number of tubes from 13 to 25, the heat distribution throughout the storage system is very effective which lead to reduction in charging and discharging times by 20% and 48% respectively.

Thermal expansion effects on the one-dimensional liquid-solid phase transition in high temperature phase change materials

Heat transfer characteristics of phase change materials (PCMs), such as the absorbed sensible and latent heat, during melting of the solid phase at constant pressure are analyzed. A model is proposed, where thermal dilation is incorporated by applying total mass conservation to materials with temperature dependent densities. A different energy-mass balance equation at the interface is obtained and shown to be a consequence of the proposed general mass conservation. Several authors have found solutions to the melting or solidification process by considering temperature dependent thermodynamic variables. In these works; however, the densities in each phase are assumed to be equal and constant. Other authors have studied the effect of having phases with different densities, but neglect the contributions of thermal dilation. To the authors knowledge, the impact of temperature dependent densities on the dynamics of the phase transition, has not been addressed. In our work, the proposed energy-mass balance equation at the interface, couples the total mass of the liquid or solid phase, to the net heat flux variation by means of an integro-differential equation. The solution of this equation and the general mass conservation presents some challenges from the numerical point of view. Semi-analytical and numerical methods are used to solve the proposed model for two types of PCMs. The solutions obtained from the proposed model are compared with predictions from other models. Depending on the type of material, it is observed that thermal expansion effects can have a significant impact on the thermal energy stored during melting.

Magnetically-accelerated large-capacity solar-thermal energy storage within high-temperature phase-change materials

Magnetically-accelerated optical charging doubles solar-thermal energy harvesting rates while fully maintaining the storage capacity of high-temperature molten salt phase change materials.

Synthesis of Al-25 wt% Si@Al2O3@Cu microcapsules as phase change materials for high temperature thermal energy storage

High temperature phase change materials (PCMs) are drawing increasing attentions globally due to their high latent heat storage ability for solar thermal energy. Encapsulation of PCMs is an effective method for preventing the leakage of liquid PCM during heat storage, which makes PCMs easier to handle. In this paper, the synthesis of microencapsulated PCM (MEPCM) with Al-25 wt% Si core (spheres, average diameter 36 µm) and Al2O3@Cu multilayered shell is reported, which works at temperature up to 500 °C. The homogeneous and effective composite shell is synthesized in multi-steps: First, a boehmite (AlOOH) shell is formed by boiling treatment in water, which is then transferred to Al2O3 shell by heating at 500 °C. Second, the Al2O3 covered particles are etched with HCl solution. Third, electroless plating of Cu layer is carried out to form the multilayered MEPCM. The surface morphology, cross-sectional structure, and thermal durability and stability of the MEPCM are investigated. The core/shell Al-25 wt%Si@Al2O3@Cu particles can maintain their integrity even after 100 melting–solidification cycles with a low breakage ratio of about 1.7%. The results indicate that as-prepared MEPCM can be used for high temperature thermal energy storage such as solar thermal power generation. The success of Cu plating on spherical particles can also be applied to fabricate other Cu coated PCMs due to expected high thermal conductivity of Cu, especially for the low temperature ones such as organic PCMs.

Encapsulation of high-temperature inorganic phase change materials using graphite as heat transfer enhancer

Abstract A quasi-isostatic pressing technique for encapsulating spherical high-temperature inorganic phase change materials (PCMs) was presented in this work. To enhance the thermal conductivity of PCMs, graphite powder was dispersed into the PCM pellets. Meanwhile, cellulose particles, as sacrificial particles, were mixed with the PCM pellets to relieve the volumetric expansion of the PCMs during the phase change process. The effects of the latent heat, thermal conductivity, and thermal expansion behavior of the PCM/graphite capsule were investigated. The PCM capsules were able to work at temperatures up to 900 °C, including undergoing a solid-liquid phase change at 803 °C with a latent heat of 159.6 J g−1, and survived more than 300 thermal cycles as thermal energy storage devices. The thermal performance of the PCM capsules between 500 and 900 °C was numerically investigated using a modified one-dimensional (1-D) enthalpy-based model. The results indicated that the average heat transfer of the PCM capsules with graphite-dispersed core was significantly elevated during both the charging (by 92.5% for 99% charge) and discharging (by 168.4% for 99% discharge) processes, compared to the pure core PCMs.

Medium- and high-temperature latent heat thermal energy storage: Material database, system review, and corrosivity assessment

Latent heat thermal energy storage refers to the storage and recovery of the latent heat during the melting/solidification process of a phase change material (PCM). Among various PCMs, medium- and high-temperature candidates are attractive due to their high energy storage densities and the potentials in achieving high round trip efficiency. Although a few review studies on high-temperature PCMs have emerged in the past few years, the quantity, completeness, and accuracy of the presented data are relatively poor. Also, an efficient indexing methodology for retrieving useful PCM data is missing in the open literature. In this article, we created an up-to-date PCM database following a holistic review of the PCMs in medium- and high-temperature applications over a temperature range of 100°C to 1680°C. Such effort then allows us to develop an accurate indexing tool for the fast selection of suitable PCM candidates and extraction of the related property data. More specifically, the created PCM database covers 496 entries of PCM materials, which are extracted from the scattered research works published during the year 1956 to 2017. The collected information includes both the basic thermo-physical properties of PCMs (eg, melting temperature, heat of fusion, and thermal conductivity) and crucial design factors during construction and engineering phases (eg, energy storage density, volume expansion, liquid/solid densities, and cost). The reviewed PCMs comprise a wide variety of materials, including fluorides, chlorides, hydrates, nitrates, carbonates, metals and alloys, and other uncommon compounds and salts. In addition, the current work presents a brief review on high-temperature latent heat thermal energy storage systems categorized into metallic and non-metallic systems. The corrosivity and stability of PCMs, which are commonly ignored in previous studies, are also examined.

Facile Synthesis of Al@Al2O3 Microcapsule for High-Temperature Thermal Energy Storage

Preparation of high-temperature encapsulated phase change materials (PCMs) is very challengeable due to the high chemical corrosion of liquid metal and the high thermal stress caused by volume expansion. We herein report a novel strategy for preparing high-temperature Al@Al2O3 PCM. In this method, nano Ni species are loaded on the surface of Al spheres, which could accelerate the oxidation of the surface Al layer during calcination in air. By monitoring the oxygen consumption and the exothermic changes during the oxidation process, it is found that the oxidation of Al follows a stepwise process which results in the formation of a layered Al2O3 shell. The high oxygen consumption and relatively low activation energy (149–156 kJ/mol) suggests that the surface nickel species significantly accelerate the low-temperature (<650 °C) oxidation of aluminum. The Al@Al2O3 composites show a well-formed core–shell structure with 60–68 wt % of core fraction, high latent heat (289–312 J/g), and mitigated supercooling per...

Synthesis of a novel three-dimensional Na2SO4@SiO2@Al2O3-SiO2 phase change material doped aerogel composite with high thermal resistance and latent heat

A novel Na2SO4@SiO2@Al2O3-SiO2 phase change material doped aerogel composite (PDAC) using the sol-gel technique is prepared. This new kind of composite material is composed of a core-shell structured Na2SO4@SiO2 phase change material (PCM) with high melting temperature and Al2O3-SiO2 aerogel with high thermal resistance and low thermal conductivity. The effects of PCM amounts and heat treatment temperatures on the physicochemical properties of Na2SO4@SiO2@Al2O3-SiO2 PDCA are investigated. X-ray diffraction (XRD) shows that when the mass percentage of Na2SO4@SiO2 PCM powders increases to 36.7%, the peaks corresponding to Na2SO4 can be well observed. The boehmite phase within Na2SO4@SiO2@Al2O3-SiO2 PDAC can be transformed to γ-Al2O3 via structural adjustment after heat treatment at 600 °C. The pore size distribution doesn’t shift after 600 °C heat treatment, and the most probable pore diameter is at around 30 nm. Transmission Electron Microscopy (TEM) shows that the Na2SO4@SiO2 PCM powders with diameters at around 500 nm can be effectively trapped and are homogeneously distributed within the aerogel matrix even after further heat treatment at 1000 °C, therefore, liquid leakage can be inhibited during melting process. The peak latent heat of Na2SO4@SiO2@Al2O3-SiO2 PDCA can be as high as 153.84 J/g with the PCM mass percentage at 36.7%. The Brunauer-Emmett-Teller (BET) specific surface area increases from 419.3 m2/g to 630.6 m2/g due to structural adjustment, and then decreases to 277.7 m2/g caused by volume shrinkage. Thermal simulation results show that the total melting time can be 254.8 s, and development of the temperature distribution keeps well with that of the liquid fraction. The velocity distribution of the liquid PCM keeps at 0 due to the constraint of aerogel matrix. This Na2SO4@SiO2@Al2O3-SiO2 PDAC can be a promising high temperature PCM in thermal energy storage applications.

An improved, generalized effective thermal conductivity method for rapid design of high temperature shell-and-tube latent heat thermal energy storage systems

Abstract To avoid full — expensive — computational fluid dynamic (CFD) simulations, latent heat thermal energy storage (LHTES) systems are often modelled by incorporating natural convection Nusselt correlations. This enables fast, coarse optimizations for phase change materials (PCMs) selection and geometrical design. While this approach is very convenient and often works well, it is frequently invoked in an ad-hoc manner — outside of known limits. To broaden the limits of applicability for this approach, this study develops natural convection Nusselt correlations for high temperature shell-and-tube LHTES systems, which are under development for concentrated solar power (CSP) plants. In these systems there is a large gap between PCM melting point and heat transfer fluid, up to 280 °C, which drives melting process. To date, many correlations that have been developed (for low temperature PCMs) in the literature are only suitable for a specific geometry and/or PCM. Therefore, this study also expands on the literature by providing correlations that are appropriate for a wide range of realistic geometric parameters and high temperature PCMs. These new natural convection Nusselt correlations were obtained by comparing the heat transfer rates in conduction only and combined conduction/convection CFD models for several PCMs and geometries in the melting process. In order to correlate the results, various sets of non-dimensional groups were subjected to a multi-variant regression analyses. The results reveal that the best fitting general Nusselt correlation can be characterized by the Rayleigh number, the Biot number, the Stefan number and the ratio of tube radius to length. The final proposed correlation has a similar shape to literature, N u N C = C R a n – however, instead of relying on empirical experimental curve fitting for C and n, this study quantifies C and n for a range of geometries/PCM properties to facilitate early design stage optimizations in the absence of experimental results.

Using renewables coupled with thermal energy storage to reduce natural gas consumption in higher temperature commercial/industrial applications

Abstract In the current study the feasibility of using solar-based renewables coupled with thermal energy storage (TES) to displace gas for heating was explored. To assess the feasibility, a numerical model of an air-based encapsulated phase change (EPCM) storage system was developed, validated, optimised, and economically costed. The optimised air-based EPCM system utilised a high and low melting temperature phase change material (PCM) with a sensible storage filler. It was found that a capsule radius of 10 mm and PCM volume of 13% resulted in the lowest cost of discharged thermal energy of $25.55/kWh when storage effectiveness and pumping power was considered. This system was then coupled to solar data for Adelaide, South Australia, to simulate the performance of a 1 MWt heat load over a year. By solving an hourly system generation and demand profile, it was found that a concentrated solar thermal (CST) and photovoltaic (PV) system coupled with TES was able to economically reduce gas consumption by 45–65% when the price of gas was $30/GJ. By employing near-term cost estimates for CST and PV systems coupled with TES, it was found that gas consumption could be reduced by similar amounts with a gas price of $20/GJ.

Utilizing blast furnace slags (BFS) to prepare high-temperature composite phase change materials (C-PCMs)

Blast furnace slag (BFS) is a typical solid waste generated in the steel production. Most of previous investigations have reported that the BFS has been used as traditional construction materials (cement, roadbed filling, concrete). In this study, a novel use route for BFS was proposed to prepare high-temperature composite phase change materials (C-PCMs) for thermal energy storage. Three typical inorganic PCMs (NaNO3, Al and Na2SO4 with different operating temperature) were blended with the pre-ground BFS to fabricate BFS-based C-PCMs by means of a mixing and sintering process. The results showed that NaNO3 had excellent chemical compatibility with BFS and the prepared C-PCMs had perfect phase change performance. The enthalpies of NaNO3/BFS C-PCMs was 65.53 J/g with melting point 300.5 °C and the super-cooling was only 0.1 °C. Furthermore, the NaNO3/BFS C-PCMs could retain good thermal reliability after 100 thermal cycles, which presented a potential application in the thermal energy storage system. In addition, the morphological structure, thermal reliability and heat transfer property of the NaNO3/BFS C-PCMs were characterised by using SEM, TGA and TG-DSC.