Salt Based Phase Change Material Research Articles

Experimental study about the impact of open cell aluminium foam (OCAF) insertion in salt-based phase change material (PCM) for electronics thermal management

Thermal management of electronic components is a critical task in a harsh thermal environment. Spacecraft and satellites' electronics are susceptible to highly intermittent heating and cooling thermal conditions, which imposes challenges for robust thermal management system design. Phase change materials (PCM) are a promising solution for overcoming these challenges and enhancing thermal control performance. The lower PCM thermal conductivity and PCM supercooling limit PCM utilisation in electronic thermal control systems. The present study aims to provide solutions for enhancing the heat transfer within the PCM, boosting the PCM thermal conductivity, and diminishing the PCM supercooling. The open-cell aluminium foam (OCAF) was adopted for boosting the heat transfer within the PCM. A thermal management module (TMM) integrated with a salt-based PCM/OCAF composite was developed for electronics thermal management. The TMM was tested under intermittent thermal conditions of heating and cooling. An electric heater and Peltier cooler were affixed to the TMM for the heating and cooling process, respectively. Three levels of heat fluxes were adopted: 700, 1000, and 1400 W/m2. The heating process lasted one hour; then, the TMM was cooled by the Peltier element to the initial temperature. The research novelty covers the gap in understanding how OCAF affects salt-based PCM supercooling when subjected to varying heating loads during intermittent cycles. The outcomes reported a remarkable improvement in thermal management efficiency. The PCM-based TMM reduced the highest temperature by about 20.4 %, 21.6 %, and 23 % at the three heating levels. The OCAF diminished the PCM supercooling curiously. The reduction in PCM supercooling was 43.5 % compared to the 100 % PCM case obtained at the heat flux of 1400 W/m2.

A novel super high latent heat ternary eutectic salt for high temperature thermal energy storage

This work is concerned with a novel ternary eutectic salt based phase change material (PCM) for high temperature thermal energy storage applications. We designed the PCM formulation in a FactSage environment and demonstrated that the formulation had a very high latent heat. The microstructure, thermal physical properties, thermal stability and cycling service life of the eutectic salt were measured experimentally with various analytical methods including scanning electron microscopy (SEM), X-ray diffractometer analysis (XRD), simultaneous thermogravimetric analyzer (STA) technique, differential scanning calorimeter (DSC) and thermogravimetric analysis (TGA). The results indicated that the eutectic salt had a melting point of 552.23 °C with a superhigh fusion enthalpy of 661.33 J/g. The change of melting point and latent heat of salt after 1500 cycles is 0.48% and 7.84%, respectively, showing excellent cycle stability.

Comparative investigation of charging performance in shell and tube device containing molten salt based phase change materials for thermal energy storage

This work concerns the melting performance enhancement in a finned shell and tube thermal energy storage device containing salt based phase change materials. Two storage materials of a pure nitrate salt and a nitrate salt based composite that made of nitrate salt, vermiculite and graphite were employed and comparatively investigated. A two-dimensional mathematical model was established to predict the heat transfer occurred in the salts by considering the combined impacts of natural convection and thermal conduction. A set of simulation data from literature was used to verify the modelling code for the pure salt and an experiment was built to validate the numerical model for the salt composite. The effects of fin amount, arrangement, length and thickness as well as operating condition on the device melting behaviour were detailedly evaluated. The results indicated the benefit of employment fins in accelerating the salt melting rate. The use of salt based composite combined with enhanced fins led to a more remarkable improvement on the device melting process, and the adjustment of fin length and thickness as well as composite ingredients composition achieved further intensification. For a given fin amounts over 0–8 with the same neighbour angle, the melting process in the device containing salt composite is respectively shortened around 79% and 56% compared to the device containing pure salt, indicating the utilization of composite is a better choice than the pure salt for the performance enhancement in finned shell and tube thermal energy storage device.

Melting Characteristics of Hybrid Nano Enhanced Phase Change Material in a Finned Circular Tube

In this study, the melting characteristics of hybrid nano-enhanced phase change material in a finned circular tube were studied by using the Finite volume method. This setup of circular tubes with a phase change material is used as cooling systems in automotive industries, air-conditioning, refrigerators, and other applications of cooling systems. There is a need for enhancing the specific heat capacity of this system to ensure that the system works even at high temperatures. As the current problem includes many design parameters and boundary constraints, the finite volume method has been performed to obtain a detailed report and data to examine the deformation of the hybrid nanoparticles and heat transfer rate on the corresponding surface. The current paper reviews and focuses mainly on the high-temperature PCM. And the suitable PCM has been selected based on its limitations and properties. To ensure the increased specific heat capacity, a salt-based phase change material, i.e., a mixture of NaNO3-KNO3 (60:40 ratio) binary salt. This PCM could hold a temperature up to 334◦C before melting to change its phase. In addition to spherical-shaped nanoparticles of silica (SiO2) in this binary salt, it tends to have a significant potential for enhancing the thermal storage characteristics of the NaNO3-KNO3 binary salt. On an extended surface, Finns are used on the peripheral of the circular tube to increase the surface area, which leads to an increase in frictional resistance resulting in a reduced airflow rate in the vicinity of the finned surface. From case studies, it has been found that the optimum fork-shaped fin array with two branches gives higher heat dissipation than the optimum rectangular fin. In the majority of the cases, the optimum fork-shaped fin array gives a 59.9% higher heat transfer rate compared to the rectangular fin array. Thus, the melting characteristics of the hybrid of NaNO3- KNO3 with nanoparticles of silica are studied when placed in a circular tube containing fork-shaped fins.

Phase transition behaviour of hydrated Glauber’s salt based phase change materials and the effect of ionic salt additives: A molecular dynamics study

Melting behaviour of inorganic hydrated salts plays an important role in their application as phase change energy storage materials. Particularly, the phase transition temperature and latent heat are determining factors for their application in specific areas for building heating. Ionic salts (e.g. NaCl, KCl) have been proposed as additives to synthesize Glauber’s salt with desired phase change properties. However, melting behaviour of the hydrated salts as well as the role of additives is poorly understood, which limits our ability to synthesize these salts with targeted properties. In the present study, classical molecular dynamics simulations were used to study the melting behaviour of pure Glauber’s salt. System of NaCl.Na2SO4.10H2O was studied to gain insights into the atomistic mechanism of the ionic salt additives. It is observed that the transition of hydrated Glauber’s salt into anhydrous Na2SO4 happens over a temperature range due to the stepwise dissociation of water molecules from the parent salt molecule. Addition of NaCl results in lowering the phase transition temperature, while increasing the latent heat of phase change at the same time. Simulation results showed that the hydrogen bonding capacity and ionic charge of the additive salts are the determining factors in altering the phase transition behaviour of hydrated salts. Simulation results showed an excellent agreement with the experimental data available in the literature.

Modified diatomite-based porous ceramic to develop shape-stabilized NaNO3 salt with enhanced thermal conductivity for thermal energy storage

Low thermal conductivity and corrosion problem of NaNO 3 salt-based phase change materials (PCMs) are regarded as two critical barriers for their applications in thermal energy storage. To address the above problem, a diatomite-based porous ceramic modified by CaCO 3 was firstly used to develop shape-stabilized NaNO 3 in this work. Particularly, contribution of modified diatomite-based ceramic on improving thermal conductivity of the composite was investigated. Compared with traditional diatomite-based skeleton, diatomite-based ceramic was found to contribute to a 129% higher thermal conductivity of composites, benefited by the generation of a dense and continuous skeleton that consisted of newly formed cristobalite phase with a higher thermal conductivity. While crack occurred on the composite with diatomite-based ceramic after 100 thermal cycles, resulting in the leakage of salt and the decrease of thermal conductivity. By contrast, diatomite-based ceramic modified by no more than 40 wt% CaCO 3 effectively avoided the crack of composites, exhibiting quite a stability in shape and thermal conductivity during 500 thermal cycles. The modified ceramic was shown to improve the thermal conductivity of loaded NaNO 3 by 118%, up to 1.22 W/(m·K) at 25 °C. The results also indicated that the modified ceramic hardly changed the phase transition temperature of NaNO 3 , but decreased the latent heat of composites, while possessed a much higher capacity to load salt (57 wt% NaNO 3 ) than that of other porous ceramics. The composite with modified ceramic was demonstrated to have a good cycling stability in thermal properties as well, which performed a considerable potential in thermal energy storage. • A modified diatomite-based ceramic was firstly used to shape-stabilize NaNO 3 salt; •Diatomite-based ceramic greatly improved thermal conductivity of loaded NaNO 3 ; •Modified ceramic avoided the crack to enhance stability of thermal conductivity; •Composites exhibited quite a stability in thermal properties in 500 thermal cycles.

A Quantitative Approach for Thermal Characterization of Phase Change Materials

Abstract A quantitative method for the calculation of phase change parameters of salt-based phase change materials (PCMs) has been proposed. This technique involves the estimation of mold-salt interfacial heat flux by solving Fourier’s law of heat conduction within the salt and using it for the calculation of phase change enthalpy of salt PCMs. Radial heat transfer was ensured by keeping the length to diameter (L/D) ratio of the mold equal to 5. The proposed method eliminates any drawbacks involved with sample size, reference material, the baseline fitting calculations, and the errors introduced due to the selection of solidification points. Pure salt PCMs such as potassium nitrate (KNO3), sodium nitrate (NaNO3), and solar salt mixture (60 wt. % NaNO3 + 40 wt. % KNO3) were used for validation of this technique. The thermal behaviors of the salt and the mold during solidification of the salt sample were analyzed, and solidification characteristics such as cooling rate, solidification time, and phase change enthalpy of PCMs were determined.

Effect of Different Production Processes on Metallic Composite Phase Change Materials for Thermal Energy Storage

Phase Change Materials (PCMs) can be applied in Thermal Energy Storage and Thermal Management systems, exploiting the storage and release of latent heat associated to a phase transition. Among them, metallic PCMs can be used at medium and high temperatures (i.e. above 150°C), storing higher heat per unit volume at higher temperatures with respect to the most widely investigated polymeric and salt-based PCMs. Miscibility Gap Alloys (MGAs) can be used to obtain multiple-phase mixtures in which the active phase (the actual PCM) is mixed to a second, high-melting temperature phase, with negligible interaction between them. These can actually be considered as fully metallic composite materials specifically developed for thermal management. Suitable microstructures can prevent leakage of active phase when the solid-liquid transition occurs, resulting in a form-stable PCM (FS-PCM). However, obtaining these microstructures it is not trivial. The present study focuses on a solid-liquid FS-PCM consisting of a ‘classical’ fully metallic FS-PCM, an Al-Sn based MGAs produced by powder metallurgy. The goal was to evaluate the effect of different production processes on thermal and mechanical behaviour of the PCM. Particularly, powder metallurgy routes including both simple mixing and ball milling were compared and further combined. Moreover, several compression and sintering conditions were considered, also substituting Al powders with Al-alloy powders, in order to optimize the material microstructures in view of suitable thermal and mechanical properties. Finally, the casting route with a rapid solidification approach was investigated for the same alloy.

T-history method: the importance of the cooling chamber to evaluate the thermal properties of Glauber’s salt-based phase change materials

Phase change materials (PCMs) are very interesting latent heat storage systems used for various thermal energy storage applications, such as in energy-conserving buildings. Both organic compounds (such as paraffins) and inorganic compounds (such as hydrated salts) were tested in this field. Since they are often heterogeneous materials because of additives, the study of their thermal properties is now addressed from the conventional calorimetry to new methods based on more significant samples to better describe the heterogeneous structure, such as the T-history method. It requires a simple and inexpensive unit, but this equipment is not commercially available and must be set up in a laboratory. Consequently, this method does not have a standard configuration and it is continuously improving. One of the critical units of the T-history-based equipment is the cooling chamber and its operating conditions, whose choice influences the results. In this work, three different cooling chambers were used in the analysis of the thermal properties of hexadecane and Glauber’s salt-based PCMs in order to verify the reliability and reproducibility of each system.

Crossed analysis by T-history and optical light scattering method for the performance evaluation of Glauber’s salt-based phase change materials

Glauber’s salt (sodium sulfate decahydrate) is a phase change material (PCM) with promising thermal and physical properties. Moreover, it is very interesting from an economic point of view because it is possible to recover it as a waste product after the disposal of lead batteries. Nevertheless, it is restricted in its applications because of supercooling and phase segregation which require suitable additives that decrease the melting temperature and latent heat of fusion. The obtained mixtures are dispersions of powders in liquids, complex energy storage systems with properties depending not only on composition but also on preparation method. This last aspect is poorly addressed in literature for PCMs. Moreover, these systems are thermodynamically unstable, therefore information about the destabilization kinetic is necessary. The thermal analysis was based on the T-history method, considered by many authors as a more suitable method than Differential Scanning Calorimeter (DSC) for heterogeneous materials, since it requires larger-size samples. Nevertheless, long-term destabilization phenomena were not sufficiently investigated in literature, but they are very relevant because they influence the dispersion stability, homogeneity and energy performances. For this same reason, an optical light scattering method, based on the use of an innovative instrument, the Turbiscan®, was proposed in this work to study the stability of such heterogeneous PCMs. Two different compositions of Glauber’s salt/borax/bentonite were prepared under controlled sonication conditions and analyzed, as a case study. Transmission and backscattering profiles were studied, explained and correlated with thermal properties and sample compositions and preparation.

Molecular dynamics simulation of thermophysical properties of NaCl-SiO2 based molten salt composite phase change materials

It is urgently needed to improve the thermal properties of molten salt based phase change materials used for effective storage and utilization of solar energy. In this paper, the physical model of NaCl-SiO2 composite phase change materials (CPCM) was established. An effective method based on molecular dynamics (MD) simulation was proposed and validated to predict the thermal properties of CPCM. The structural deformation during phase transition process of CPCM system was observed and the radial distribution function (RDF) was calculated to analyze the local structure. The results indicate that the thermal conductivity of NaCl is enhanced remarkably with a maximum increase of 44.2% by adding 2.4% volume fraction of SiO2 nanoparticles and the mechanism of the thermal conductivity enhancement was discussed at the atomic level. The shear viscosity increases with the increase of the volume fraction of nanoparticles, with a maximum average increase of 23.6%. The relationship between self-diffusion coefficient and temperature is approximate to predict melting point. The force field and simulation methods adopted in this paper are desired to be useful for the prediction of thermal properties and further investigation into molten salts based thermal energy storage systems.

Heat transfer performance of thermal energy storage components containing composite phase change materials

This study concerns about the heat transfer behaviour of composite phase change materials (CPCMs) based thermal energy storage components. Two types of components, a single tube and a concentric tube component, are designed and investigated. The CPCMs consist of a molten salt based phase change material, a thermal conductivity enhancement material (TCEM) and a ceramic skeleton material. A mathematical model was established to model the heat transfer behaviour. The modelling results were first compared with experiments and reasonably good agreement with the experimental data was obtained, demonstrating the reliability of the model. Extensive modelling studies were then carried out under different conditions. The influence of thermoproperties, surface roughness and size of the CPCMs as well as heat transfer fluid (HTF) velocity were examined. The results show that the thermal contact resistance between the CPCMs should be considered. Increasing the mass fraction of TCEMs and thickness of CPCMs as well as the HTF velocity intensifies the heat transfer behaviour of component. The concentric tube based component offers a better heat transfer performance compared with the single tube based component, with the total heat storage and release time ∼10 and 15% shorter, respectively, for a given set of conditions.

Experimental investigation on phase change material based thermal storage system for solar air heating applications

Many types of solar air heaters have been developed in India and their performance has been studied in detail. In solar dryers the drying process largely depends on the varying local weather conditions, resulting in a poor quality of the dried product. To eliminate the fluctuations in the temperature of the hot air, solar collectors are integrated with the Phase Change Material (PCM) based thermal storage unit. The present study is aimed at investigating the feasibility of using a latent heat storage unit with HS 58, an inorganic salt based phase change material, to store the excess solar energy, and release it when the energy availability is inadequate during poor weather conditions, and to extend the period of utilisation beyond the sunshine hours. Experiments were conducted to evaluate the charging and discharging characteristics of the storage unit. The effects of inlet flow rate during the charging and discharging processes were measured and reported. For the storage tank configuration and PCM ball size considered in the present investigation, the mass flow rate of 200kg/h is able to provide a near uniform rate of heat transfer during charging and discharging processes. Further, low mass flow rate is able to utilise the maximum capacity of the storage system and to supply heat for a longer duration.