Solid-liquid Phase Change Research Articles

Effect of PCM melting temperature on solar ponds performance: Design and experimental investigation

Salt gradient solar pond (SGSP) is a technology which uses a renewable source such as solar energy to store thermal energy in a saline solution. Traditional SGSPs work in the sensible zone, increasing its temperature as the solar radiation is absorbed. SGSPs suffer from a low stability and energy efficiency, mainly caused by the high temperatures reached. At high temperatures, higher heat losses correspond. PCMs are characterized by high latent heat and a solid-liquid phase change at a nearly constant temperature. A pond integrated with PCMs can store the same amount of energy at a lower temperature, improving thermal efficiency and stability. In this paper, a pond integrated with PCM (RT35 HC) and a traditional one were designed, built and tested to evaluate the different performance. According to results, over ten days, the average temperature in the pond with the RT35 HC is about 4 °C lower (corresponding to the 5.7 %). Then a second experimental analysis was conducted comparing two different melting temperatures (RT35 HC and RT44 HC). Results show that a higher melting temperature enables to smooth the high peaks of temperature. While a lower melting temperature guarantees a higher and more stable temperature at night, due to the release of latent heat, making the application useful in case of constant temperature demand at the outlet fluid. Results are widely discussed in the paper.

Pore scale simulation for melting of composite phase change materials considering interfacial thermal resistance

• Implicit-enthalpy-based LBM with interfacial thermal resistance is proposed. • Porous structure is reconstructed by randomly generation-growth method. • The effective thermal conductivity of composite PCMs is evaluated. • The effect of natural convection, porosity and interface on melting are analyzed. The convective melting process and thermal performance of phase change materials (PCMs) incorporating porous skeleton in the one-side-heated rectangular cavity are investigated numerically in this work. A pore-scale lattice Boltzmann method (LBM) with implicit scheme is developed to explore the solid–liquid phase change process. The interfacial thermal resistance between the skeleton and PCMs is considered by interfacial conditions treatment. The random porous microstructure is generated by quartet structure generation set (QSGS) which is used to compute effective thermal conductivity in LBM. The validations of the current model are employed by the two-phase series conduction model and previous numerical results. The effects of porous structure, skeleton material, and thermal interfacial conditions on heat transfer characteristics are systematically investigated. The computational results show that the melting rate and effective thermal conductivity increase with the reducing porosity and the high thermal conductivity of the skeleton material accelerate the melting process. In addition, the consideration of interactions in the LBM leads to a significant difference. When the thermal interfacial resistance is set to be 1 × 10 −4 m 2 W/K, the temperature drop is very large in two-phase conduction, the melting rate decreases remarkably in the phase change process. The present simulation is also suitable for optimizing the porous structure to prepare various composite PCM in the thermal energy storage field.

A Photovoltaic Panel Integrated with Phase Change Material as Peak Shaving for Domestic Hot Water Energy Demand

Phase change materials (PCMs) applied to photovoltaic (PV) panels are a promising solution to recover the large share of energy from the incident radiation, not converted into electricity. PCMs can store a huge amount of energy, exploiting the solid-liquid phase change, which occurs at a nearly constant temperature. In addition, reducing the temperature of a PV panel increases its electric conversion efficiency. This papers experimentally investigates the match between the heat production of a PV-PCM system and the domestic hot water (DHW) demand of a typical residential building. Different curves of demand are analyzed, all have a peak in the evening period. The solar radiation profile of a typical sunny day is reproduced under a solar simulator. Once the PCM is fully melt, a hydraulic circuit, which connects the heat exchanger immersed in the PCM to a water tank, is activated to extract the heat stored. Different tests are performed by varying the size of the water tank storage. Results show that a storage volume of 50 L, 75 L, 100 L and 125 L ensures a reduction of energy demand of 15.3%, 21.2%, 22% and 21.5% respectively, compared to traditional electric water heaters.

Thermophysical properties of LiF–LiCl–Li2CO3 eutectic mixture/multi-walled carbon nanotubes for thermal energy storage

Latent heat thermal energy storage based on solid-liquid phase change material has a huge potential in dealing with mismatch between energy demand and supply. LiF–LiCl–Li 2 CO 3 ternary system was screened out for high temperature energy storage material due to its good thermophysical properties. Its eutectic composition ( X LiF = 28.41 mol%, X LiCl = 55.09 mol% and X Li2CO3 = 16.50 mol%) was predicted based on the developed thermodynamic model and verified experimentally. The melting point, phase change latent heat, heat capacity, thernal diffusivity, thermal conductivity and thermal stability of LiF–LiCl–Li 2 CO 3 eutectic mixture were measured. And the influence of the addition of multi-walled carbon nanotubes (MWCNTs) were analyzed. It was found that adding MWCNTs could increase the latent heat, specific heat capacity, thermal diffusivity and thermal conductivity of LiF–LiCl–Li 2 CO 3 eutectic mixture, while didn't significantly change the melting temperature. • An innovation molten salt is successfully designed via computational thermodynamic approach. • Thermophysical properties of the eutectic salt are determined experimentally. • Composite phase change material (CPCM) was prepared and characterized. • Thermal conductivity and heat capacity can be enhanced by doping nanoparticles.

A novel thermoelectric energy harvester using gallium as phase change material for spacecraft power application

Thermoelectric generator (TEG) integrated with phase change material (PCM) is suitable for spacecraft power supply under environment with extreme temperature variation, but the low solid–liquid phase change rate restrains system performance. To increase output energy and thermoelectric conversion efficiency, a novel thermoelectric energy harvester (TEH) integrating TEG with gallium (Ga) is proposed. A numerical model for predicting system performance is established, and validated by experimental results. The open circuit voltage (U), maximum output power (Pmax), output energy (E) and thermoelectric conversion efficiency (η) for Ga-TEH system under microgravity and normal gravity with environment temperature ranging from 100 to −50 °C are investigated. The results show that compared with TEH using conventional PCM n-octadecane (C18), the adoption of Ga significantly improves system performance due to higher heat conduction ability and larger volumetric latent heat of Ga; U, Pmax and η for Ga-TEH are maximally 9.5, 101.8 and 12.7 times those for C18-TEH under microgravity respectively, and maximally 7.3, 58.7 and 9.4 times those for C18-TEH under normal gravity respectively; E for Ga-TEH are 9.9 and 9.0 times those for C18-TEH under microgravity and normal gravity respectively. The designed Ga-TEH can be used for wireless sensor networks power supply in spacecraft.

Development of temperature-responsive transmission switch film (TRTSF) using phase change material for self-adaptive radiative cooling

To overcome the problem of unable automatic turn on and off response to the ambient temperature of current static radiative cooling systems, we prepared a series of temperature-responsive transmission switch film (TRTSF) samples using n-octadecane as phase change material (PCM) and polydimethylsiloxane (PDMS) as carrier material. The phase change cycle permeability analysis showed that the TRTSF samples with PCM content above 30.0 w.t.% exhibit a serious leakage problem due to a large number of holes on surface. The TRTSF samples with 10.0–30.0 w.t.% PCM content were further analysed by Differential scanning calorimetry (DSC) and Thermogravimetry (TG), and compared with the theoretical PCM contents, which verified the reliability of the curing results of PCM in TRTSF from various aspects. The ultraviolet–visible light-near-infrared (UV–VIS-NIR) and mid-infrared (MIR) transmittance characterization of TRTSF revealed that the switching effect was obvious during solid–liquid phase change process. TRTSF microstructure analysis revealed that the particle size distribution of PCM microspheres was between 1 μm and 6 μm. The UV–VIS-NIR band (wavelength at 0.25–1.1 μm) transmittance of PCM decreased to less than 3.7% after solidification due to the interfacial reflectance of solid PCM particles increased to more than 66.8% even in monolayer, thus the solid PCM particles would produce Mie scattering and isolate the internal and external radiation heat transfer. However, the TRTSF can be used as the radiative cooling emission layer since its optical properties were similar to the PDMS when the PCM is in liquid phase. Overall, the TRTSF film prepared in this study successfully adapted the temperature switching properties, also, is expected to be further used for the development of self-adaptive radiative cooling systems.

A Liquid Metal-Enhanced Wearable Thermoelectric Generator.

It is a key challenge to continuously power personal wearable health monitoring systems. This paper reports a novel liquid metal-enhanced wearable thermoelectric generator (LM-WTEG that directly converts body heat into electricity for powering the wearable sensor system. The gallium-based liquid metal alloys with room-temperature melting point (24~30 °C) and high latent heat density (about 500 MJ/m3) are used to design a new flexible finned heat sink, which not only absorbs the heat through the solid-liquid phase change of the LM and enhances the heat release to the ambient air due to its high thermal conduction. The LM finned is integrated with WTEG to present high biaxial flexibility, which could be tightly in contact with the skin. The LM-WTEG could achieve a super high output power density of 275 μW/cm2 for the simulated heat source (37 °C) with the natural convective heat transfer condition. The energy management unit, the multi-parameter sensors (including temperature, humidity, and accelerometer), and Bluetooth module with a total energy consumption of about 65 μW are designed, which are fully powered from LM-WTEG through harvesting body heat.

Solid-liquid phase change subjected to unipolar charge injection from a circular wire electrode

A numerical investigation of isothermal melting of a dielectric phase change material in a square cavity subjected to unipolar charge injection from a circular wire electrode is reported. Governing equations for the solid-liquid phase change under the influence of an electric field include the Navier–Stokes equations for fluid flow, energy equation for thermal transport, Poisson equation for electric potential, and the Nernst-Planck equation for charge conservation. An enthalpy source-term based fixed grid approach is adopted to model the melting process. The governing equations that consider the coupled interactions between flow, thermal and electric fields are solved using the finite volume framework of OpenFOAM®. Time evolution of the melting rate, maximum flow velocity, mean Nusselt number, and mean Coulomb force in the electrohydrodynamic flow assisted melting process is mapped. The mechanism and role of electrohydrodynamic forces on influencing the net flow and melt interface morphology is studied. The competing viscous, buoyancy, and electric forces result in an altered flow pattern that aids the melting process. The enhancement in the rate of melting at different strengths of buoyancy and electrostatic forces is quantified. Furthermore, the effects of the radius of the circular wire electrode in relation to the cavity size are highlighted. A maximum of 63% enhancement in melting rate is observed within the considered parameter space.

Graphene-pentaerythritol solid–solid phase change composites with high photothermal conversion and thermal conductivity

The use of phase change materials (PCMs) with high energy storage density is an ideal method to solve the problem of uneven and discontinuous of solar energy. At present, the common phase change media are mainly low-temperature solid–liquid phase change materials (SL-PCMs), which have shortcomings such as easy leakage, low thermal conductivity (TC), and low photothermal conversion performance. In response to these problems, a research idea of using pentaerythritol (PE) as a solid–solid phase change heat storage medium and gallic acid-modified graphene nanosheets (GNPs) as light absorbers and thermally conductive filler was proposed in this paper. The results showed that the composite phase change materials (CPCMs) containing 15 wt% GNPs had the highest photothermal conversion efficiency, reaching 93.86%, which was 247.76% higher than that of PE, and the latent heat of phase change was 190.88 J/g. Compared with PE (TC is 1.02 W/(m·K)), the TC of 15 wt% GNPs-CPCMs reached 3.86 W/(m·K), which increased by 278.43%. At the same time, their phase-change temperature remained at a medium–high temperature around 185 °C, and the UV–Vis spectra showed that the CPCMs also had high absorbance under visible light. This suggested that solid–solid composite phase change materials (SS-CPCMs) with high absorbance and TC provided a new approach for solar photothermal conversion and storage.

Enhanced thermal performances of PCM heat sinks enabled by layer-by-layer-assembled carbon nanotube–polyethylenimine functional interfaces

Rationally designed hybrids of heat sinks (HSs) and phase change materials (PCMs) can mutually complement their fundamental limitations. However, integrating PCMs into HSs inevitably incurs additional thermal resistances and degradation during solid–liquid phase transitions owing to unstable contact interfaces. Herein, we report layer-by-layer (LbL)-assembled multiwalled carbon nanotube (MWCNT)–polyethyleneimine (PEI) functional interfaces between the PCM and HS surfaces to enhance thermal management capabilities. The LbL process used in this study involves direct fabrication of electrostatically adhered nanocoatings of multiple materials via a solution process, which resulted in facile formation of MWCNT-PEI percolation networks on an aluminum HS. The PCM-HS was completed by filling the HS channels with a PCM (n-eicosane). The functional interface increased the active surface areas for thermal transport and optimized the porous structures for the stabilization of the PCM–HS boundary under repetitive solid–liquid phase changes. Comparison of the fabricated specimens (bare and PCM-filled HSs without LbL interfaces) elucidated the enhanced thermal performances in transient-static operating conditions. This was confirmed by experimentally measuring the real-time temperature responses at various levels of heating power and the time delays to reach the set point temperatures, indicating a more than 10% improvement in effectiveness using the LbL interface. Furthermore, the LbL interfaces efficiently alleviated thermal shock or overload under intermittent thermal loads. The developed LbL interface offers a tunable–scalable method to fabricate PCM-filled HSs with advanced thermal properties that cannot be achieved using a conventional HS.

Thermo-physical studies and corrosion analysis of caprylic acid–cetyl alcohol binary mixture as novel phase change material for refrigeration systems

This study aims to prepare a stable caprylic acid (CA) and cetyl alcohol (CAL) organic binary mixture as a solid–liquid phase change material (PCM) with a phase transition temperature in the range for exotic chilled refrigeration. A detailed study was carried out on the thermo-physical properties, thermal reliability and corrosion analysis of the prepared binary mixture. The result showed that the binary mixture of caprylic acid–cetyl alcohol (CA–CAL) with a eutectic point at 85:15 molar mass ratio is suitable for medium-range refrigeration application. The determined onset melting/freezing temperature with differential scanning calorimetry (DSC) was 10 °C/8.9 ± 0.1 °C with a phase transition enthalpy of 154.1/153.3 ± 1% J/g. The binary mixture thermal conductivity measured in the solid phase (at 0 °C) and liquid phase (at 20 °C) was (0.288 ± 0.028) and (0.156 ± 0.007) W/(m⋅K), respectively. Moreover, the thermal reliability test result of the prepared binary mixture under accelerated thermal cycling for 500 melting/freezing cycles showed a maximum of 10.1% deviation in thermal properties, which was in the acceptable range for organic binary PCM. The prepared PCM was found to be compatible with stainless steel and aluminum over an extended period of time, based on corrosion tests conducted on aluminum, copper and stainless steel over a period of 84 days. According to this study, the binary combination CA–CAL as PCM is a potential candidate for cold chain food transportation, supermarket cold cabinets, and other refrigeration applications.

Activated carbon nanotube/polyacrylic acid/stearyl alcohol nanocomposites as thermal energy storage effective shape-stabilized phase change materials

Stearyl alcohol (SA) as one of organic phase change materials (PCMs) has promising thermal energy storage prospective. However, the leakage issue during solid-liquid phase change period and low heat harvesting and releasing rate significantly attenuates its TES potential. Towards to overcome these drawbacks, the SA was shape-stabilized using the cross-linked poly acrylic acid (PAA) and activated single walled carbon nanotubes (a-SWCNTs) at three different weigh ratio of 1:1:2, 1:3:4 and 1:5:6 (a-SWCNTs:PAA:SA). The chemical/crystalline and morphologic structures of the produced shape stabilized-nano composite PCMs (SS-NCPCMs) were investigated by FT-IR, XRD and SEM analyses. The latent heat storage (LHS) features and thermal stability of the SS-NCPCMs were measured by DSC and TGA techniques. The thermal cycling effect on the LHS properties and chemical structures of the SS-NCPCMs was also estimated. The DSC findings indicated that the SS-NCPCMs had melting temperature of around 55–56 °C and latent heat capacity of about 135 J/g. TGA measurements disclosed that the thermal degradation temperatures of the nano composite PCMs were prolonged somewhat compared to the SA. A 500 heating-cooling cycling test revealed that the SS-NCPCMs had great chemical and LHS stability. The heat harvesting and releasing performance of the NCPCMs were considerably shortened compared to those of pure SA. The obtained results exposed that the synthesized SWCNTs/PAA/SA composites can be evaluated as promising LHS materials for thermal management of electronic systems, automobile modules, food carriers, solar PV panels etc.

Fabrication of Sn@SiO2 core-shell microcapsules with high durability for medium-temperature thermal energy storage

Phase change materials (PCMs) using metals/alloys have been concerned for medium temperature solar thermal storage and waste heat recovery. However, the PCMs may leak due to the solid-liquid phase change, which greatly limits the use of metallic PCMs. In this study, we report the synthesis of microencapsulated PCMs (MEPCMs) using metallic Sn as PCM core and a sol-gel coated SiO2 as shell. The as-coated microcapsules are further undergone a high temperature heat treatment at oxygen/nitrogen atmosphere. Due to the self-repairing effect, the cracked microcapsules can be sealed and stabilized, thereby forming high stabilized MEPCMs over 100 cycles. The melting point and latent heat of the [email protected]2–O2 microcapsules were around 233 °C and 56 J g-1 respectively, while the values were around 233 °C and 58 J g-1 for [email protected]2–N2 microcapsules, similar to the theoretical values of metallic Sn. The successfully prepared [email protected]2 MEPCMs could find wide applications in medium temperature thermal energy storage.

Peak load shifting control on hot water supplied from district heating using latent heat storage system in apartment complex

District heating has been widely implemented in residences because of its environmental and economic advantages. The hot water load of residences generally peaks in the morning and at night because of the lifestyle of the residents. An imbalance in the heat load presents high capital costs and low operating efficiency of the district heating facilities. In this study, a latent heat storage system using a solid-liquid phase change material was developed for the peak load shifting control of hot water supplied from district heating in an apartment complex. The latent heat storage system was designed using a shell-tube structure and can store heat for more than 100 h using an insulation of 50 mm. A field demonstration was performed by installing the developed latent heat storage system in a machinery room in the basement of the apartment complex. The demonstration showed that the total heat flow of hot water during a day and its standard deviation with the latent heat storage are lower than those without latent heat storage by 2.69% and 59.9%, respectively. Therefore, the latent heat storage system is crucial in the peak load shifting of hot water in the apartment complex.

Melting assessment on the effect of nonuniform Y-shaped fin upon solid–liquid phase change in a thermal storage tank

This study provides an alternative solution to the improvement on solid–liquid phase change by designing a Y-shaped fin in a nonuniform pattern along the gravity direction. A numerical model is established and validated through the present measurement and data in literature. Six cases with different Y-shaped fins and locations are designed and compared to the original straight fin case. Thermal assessments on the melting fraction, temperature field, velocity distribution, and uniformity for melting are made. Results demonstrate that the nonuniform melting features caused by the local natural convection are significantly eliminated by the novel nonuniform fin structure. The time required for melting the lower PCM is found to occupy more than 50% of the completely melting time. The accurate local heat transfer enhancement measures (bottom enhancement) are conducive to markedly reduce the full melting time by 21.5%, compared to the uniform fin pattern. Upon using finned thermal storage tank for a mobilized thermal storage truck (bare tube tank), the initial investment increases by 44.9% but the profit increases by 393.6% and the payback period reduces by 69.2%. The use of fin tube in heat storage tank can quickly obtain higher returns based on a small increase in initial investment. This work provides new insights into the understandings of the transient phase change process and the strategies for guiding the design for thermal energy storage tank.

Role of natural convection and battery arrangement for phase change material based battery thermal management unit

Phase change material (PCM) based battery thermal management (BTM) has been of increasing interest due to the passive concept with efficient cooling and temperature uniformity performance. Due to the inherent characteristics of solid-liquid phase change during operation, it is worth in-depth investigation of the influence of buoyancy driven natural convection (NC) on battery thermal behavior. Here, a typical PCM enclosed cylindrical battery unit is considered as the benchmark problem. The effects of battery arrangement and liquid PCM NC on melting process and thermal performance are investigated numerically based on rigorously validated model. It shows that excellent cooling performance could be achieved for battery with the function of latent heat storage of PCM, whether the unit is arranged vertically or horizontally. In addition, the horizontal arrangement (4.1 K) has a better temperature uniformity than the vertical arrangement (5.7 K), which can be ascribed to the varying melting rate of PCM. To further insight into the thermal behavior of BTM unit, the relationship between the melting rate and interface length associated with differential liquid fraction curve is proposed for the first time. When the liquid PCM is full of the upper half of the BTM unit, the length reaches its maximum value and after that the differential liquid fraction is significantly declined, indicating the poor heat transfer and thermal performance. The motivation is to not only explore the fundamental mechanism of passive phase change method, but also to serve as a basis for the design of more practical and efficient PCM based BTM in the future.

Thermodynamically predicting liquid/solid phase change of long-chain fatty acid methyl esters (FAMEs) and its application in evaluating the low-temperature performance of biodiesel

BackgroundLong-chain FAMEs, also called biodiesel, are viewed as the alternative to petroleum diesel for renewability and sustainability. Because the fatty acid profiles significantly varied for the sources, the compositions significantly affected the biodiesel properties, such as cloud points. The cloud point of biodiesel indicates the phenomenon of solid-liquid phase change. Previous models for cloud point predictions were limited to known components in the mixtures. MethodsThe cloud points of the binary, ternary and multicomponent mixtures of fatty acid methyl esters were measured in this study. A cloud point prediction model was established based on phase equilibrium with the modified Universal functional activity coefficient (UNIFAC) model and excess fusion enthalpy for predicting the nonideal behaviors of the components resulting from the molecular shape and molecule interactions. Significant findingsThe developed thermodynamic model accurately predicts the cloud point according to compositions. The model extends the application scope to the low-temperature range. There had eutectic points in the phase diagrams when the mixtures consisted of either saturated FAMEs or unsaturated FAMEs. This study proved that saturated FAMEs regulate the cloud points, but unsaturated FAMEs affect them through group interactions. Moreover, the proposed model can predict unknown FAMEs mixture as it is built on the group contributions.

Phase Change Material numerical simulation: enthalpy-porosity model validation against liquid fraction data from an X-ray computed tomography measurement/system

ABSTRACT Nowadays, Latent Thermal Energy Storage systems (LTESs) are becoming the key enabling technology for the achievement of the 2050 EU targets on energy savings and CO2 emission reduction. LTESs are based on Phase Change Materials (PCMs), which, during the liquid-solid phase change, can store and release large amount of thermal energy compared to sensible systems. Several studies have already been conducted to properly design LTESs based on PCMs and many of those aimed at developing reliable numerical tools. The main approach to model the phase change with a Computational Fluid Dynamics (CFD) approach is the enthalpy-porosity method, which has already been successfully validated in several articles, especially against the average PCM temperature. However, due to the experimental complexity, the liquid fraction evolution is hard to be measured and monitored and only symmetrical systems could have been tested so far. X-ray Computed Tomography (CT) is a strong and reliable tool to experimentally evaluate the liquid fraction profile during either the melting or solidification process in real geometries and is extremely useful to validate the numerical models. In the present study, a first attempt to combine the described experimental-numerical approach is proposed: an enthalpy-porosity model was developed and validated against liquid fraction data from a computed tomography system. The liquid fraction profile of an ice cylinder melting at ambient temperature was measured using the CT and then compared against the numerical results. The results show the promising capabilities of the proposed methodology.

Mussel-inspired strategy to construct 3D silver nanoparticle network in flexible phase change composites with excellent thermal energy management and electromagnetic interference shielding capabilities

Nowadays, efficient thermal management and electromagnetic interference shielding as effective measures for maintaining the normal operation of electronic devices are extremely significant. However, composites with both thermal management and electromagnetic interference shielding performance are rarely reported. In this study, a kind of flexible polydopamine (PDA) and silver nanoparticles (AgNPs) wrapped melamine foam (MF) constructed by adopting the mussel-inspired strategy was used to fabricate MPAχ-PEG phase change materials (PCMs) via encapsulating polyethylene glycol (PEG). PDA was selected to enhance the interface bonding between MF and AgNPs due to its strong adhesion based on mussel-inspired surface chemistry. Continuous AgNPs wrapped on skeleton of MF construct the three-dimensional (3D) thermal/electrical-conductive porous network. MPAχ-PEG PCMs exhibit a relatively high phase change enthalpy of 148.9 J/g and a high thermal conductivity enhancement of 1400% in comparison with that of MF-PEG. Moreover, MPAχ-PEG PCMs are provided with electromagnetic interference (EMI) shielding performance with the mean SET of 82.02 dB and electro-to-thermal energy conversion efficiency (86.3% under the voltage of 1.2 V) due to the 3D conductive AgNPs network. Combining the elasticity of MPAχ foams and the phase change feature of PEG, the MPAχ-PEG PCMs show good solar-induced shape memory performance. The flexible PCMs could avoid the sharp temperature increase of smartphone by the solid-liquid phase change process of PEG. Therefore, this study provides a promising strategy to prepare flexible PCMs, which can achieve various forms of energy conversion, as well as thermal management and EMI shielding performance, can definitely broaden their application prospect in electronic devices.

Design optimization and thermal storage characteristics of NaNO3-NaCl-NaF molten salts with high latent heat and low cost for the thermal energy storage

NaNO3-NaCl-NaF salts were investigated by thermodynamic calculation and experimental measurement. A set of self-consistent thermodynamic parameter for the NaNO3-NaCl-NaF salts was finally obtained, by which the predicted melting point (i.e., 288.2 °C) is in excellent agreement with the experimental value (i.e., 288.0 °C). The actual eutectic point of the NaNO3-NaCl-NaF salts is placed at 288.0 °C and XNaNO3 = 0.905 mol, XNaCl = 0.059 mol, and XNaF = 0.036 mol. The fusion enthalpy of the NaNO3-NaCl-NaF salts is 210.0 J/g, and the average liquidus specific heat capacity is 1.760 ± 0.030 J/g·°C. Weight loss is only 5.0 wt% at 650 °C, and its thermal stability is high. The fusion enthalpy is increased by 86.7% than that of NaNO3-KNO3 and 252.0% than that of NaNO3-NaNO2-KNO3. Furthermore, the cost of storage solid-liquid phase change heat of the NaNO3-NaCl-NaF salts is only 50% of that of NaNO3-KNO3 salt and 25% of that of NaNO3-NaNO2-KNO3 salts. The developed NaNO3-NaCl-NaF eutectic salts has relatively superior thermophysical properties, suitable working temperature and good economy performance, and can be used as one of the candidate thermal energy storage fluids. This work provides fundamental reference for the selection of thermal energy storage materials and enriches molten salts databases.