scholarly journals OBTAINING AND PROPERTIES OF NANOSCALE SOLID-STATE HEAT STORAGE WITH CARNAUBA WAX

Author(s):  
S.Ya. Brichka

Latent thermal energy storage using phase change materials has attracted interest in the use of solar and other types of energy due to their ability to provide high density lateral energy storage. Materials with a latent heat of storage have become attractive for their use in many branches of human activity. However, the materials use is often limited by problems of low thermal conductivity, the transition from a solid to a molten state causes difficulties in storing materials in a container, and special heat exchangers are needed to increase the energy cost. The solution to the above problems may be to create solid-state, form-stable heat storage elements. In this work, a number of shape-stable materials with a phase transition were obtained from melts by mixing halloysite nanotubes with carnauba wax in order to improve the heat accumulation characteristics. Halloysite nanotubes were mixed at elevated temperatures with carnauba melted wax and rapidly cooled to prevent the nanotubes sedimentation. As a result, a series of solid wax/nanotube samples were prepared with weight ratios of 70/30, 60/40 and 50/50. Pure wax showed a accumulation heat of the solid-to-liquid phase transition of 189.09 J/g. Carnauba wax has a latent heat greater by about 25 % compared to paraffin. Composite materials had significantly lower latent heat, respectively, 99.39 J/g for 70/30, 90.25 J/g for 60/40, and 81.26 J/g for 50/50 samples. Elemental mapping of the nanomaterial revealed a nanotubes uniform distribution in the wax. According to the data of X-ray analysis, as a result of the composite materials preparation, the components did not form new crystalline phases, but they were physical mixtures. When heated, the components did not chemically interact with each other, which is useful for the accumulation of thermal energy by materials. Analysis of the IR spectra of the samples confirmed the change in the absorption bands of functional hydroxyl groups at 3696 sm–1 (Al–O–H) and 3621 sm–1 (Si–O–H). In primary nanotubes, the intensities ratio of silanol to aluminol groups is greater than unity, while in the composite it is already less than this value. This manifestation can be explained by the fact that, during the wax melting, the interaction of wax molecules on the outer surface of the nanotubes occurs. Bibl. 16, Fig. 5.

2021 ◽  
Vol 13 (5) ◽  
pp. 2685
Author(s):  
Mohammad Ghalambaz ◽  
Jasim M. Mahdi ◽  
Amirhossein Shafaghat ◽  
Amir Hossein Eisapour ◽  
Obai Younis ◽  
...  

This study aims to assess the effect of adding twisted fins in a triple-tube heat exchanger used for latent heat storage compared with using straight fins and no fins. In the proposed heat exchanger, phase change material (PCM) is placed between the middle annulus while hot water is passed in the inner tube and outer annulus in a counter-current direction, as a superior method to melt the PCM and store the thermal energy. The behavior of the system was assessed regarding the liquid fraction and temperature distributions as well as charging time and energy storage rate. The results indicate the advantages of adding twisted fins compared with those of using straight fins. The effect of several twisted fins was also studied to discover its effectiveness on the melting rate. The results demonstrate that deployment of four twisted fins reduced the melting time by 18% compared with using the same number of straight fins, and 25% compared with the no-fins case considering a similar PCM mass. Moreover, the melting time for the case of using four straight fins was 8.3% lower than that compared with the no-fins case. By raising the fins’ number from two to four and six, the heat storage rate rose 14.2% and 25.4%, respectively. This study presents the effects of novel configurations of fins in PCM-based thermal energy storage to deliver innovative products toward commercialization, which can be manufactured with additive manufacturing.


2019 ◽  
Vol 141 (5) ◽  
Author(s):  
S. Arunachalam

Energy storage helps in waste management, environmental protection, saving of fossil fuels, cost effectiveness, and sustainable growth. Phase change material (PCM) is a substance which undergoes simultaneous melting and solidification at certain temperature and pressure and can thereby absorb and release thermal energy. Phase change materials are also called thermal batteries which have the ability to store large amount of heat at fixed temperature. Effective integration of the latent heat thermal energy storage system with solar thermal collectors depends on heat storage materials and heat exchangers. The practical limitation of the latent heat thermal energy system for successful implementation in various applications is mainly from its low thermal conductivity. Low thermal conductivity leads to low heat transfer coefficient, and thereby, the phase change process is prolonged which signifies the requirement of heat transfer enhancement techniques. Typically, for salt hydrates and organic PCMs, the thermal conductivity range varies between 0.4–0.7 W/m K and 0.15–0.3 W/m K which increases the thermal resistance within phase change materials during operation, seriously affecting efficiency and thermal response. This paper reviews the different geometry of commercial heat exchangers that can be used to address the problem of low thermal conductivity, like use of fins, additives with high thermal conductivity materials like metal strips, microencapsulated PCM, composite PCM, porous metals, porous metal foam matrix, carbon nanofibers and nanotubes, etc. Finally, different solar thermal applications and potential PCMs for low-temperature thermal energy storage were also discussed.


Energies ◽  
2020 ◽  
Vol 13 (19) ◽  
pp. 5024
Author(s):  
Xiaoling Cui ◽  
Xiaoyun Du ◽  
Yanzhou Cao ◽  
Guochen Sang ◽  
Yangkai Zhang ◽  
...  

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.


2018 ◽  
Vol 2018 ◽  
pp. 1-13 ◽  
Author(s):  
Qianjun Mao ◽  
Ning Liu ◽  
Li Peng

Solar thermal energy storage (TES) is an efficient way to solve the conflict between unsteady input energy and steady output energy in concentrating solar power plant. The latent heat thermal energy storage (LHTES) system is a main method of storing thermal energy using phase change materials (PCMs). Thermal properties, that is, melting points and latent heat, are the key parameters of PCMs for the TES system. In this paper, the PCMs are classified into inorganic and organic by the chemical composition, and according to the melting point, the inorganic PCMs can be divided into three contributions: low-temperature heat storage (less than 120°C), medium-temperature heat storage (120–300°C), and high-temperature heat storage (more than 300°C). The present article focuses mainly on the recent investigations on the melting point and latent heat of PCMs via DSC setup in the solar TES systems. The results can provide a good reference for the selection and utilization of PCMs in the solar TES systems.


Materials ◽  
2021 ◽  
Vol 14 (20) ◽  
pp. 6032
Author(s):  
Bo Yang ◽  
Yang Liu ◽  
Wenjie Ye ◽  
Qiyang Wang ◽  
Xiao Yang ◽  
...  

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.


Materials ◽  
2019 ◽  
Vol 12 (22) ◽  
pp. 3658 ◽  
Author(s):  
Stefania Doppiu ◽  
Jean-Luc Dauvergne ◽  
Angel Serrano ◽  
Elena Palomo del Barrio

In this paper, the system Li2SO4–Na2SO4 is proposed as a candidate material for thermal energy storage applications at high temperatures (450–550 °C). Depending on the composition, the thermal energy can be stored by using a eutectoid reaction and solid–solid phase transition. In these types of systems, all the components (reagent and products) are in the solid state. This work includes the theoretical analysis (based on the Calphad method) of the system selected obtaining all the theoretical parameters (for example, enthalpies of reaction, transition temperatures, volume expansion, and the heat capacities) necessary to determine the theoretical performance in terms of thermal energy storage. The theoretical analysis allowed to identify two compositions (Li2SO4/Na2SO4 79/21 and 50/50) in the phase diagram with the most promising theoretical enthalpy of transformation (270 J/g and 318 J/g, respectively) corresponding to a eutectoid reaction and a solid–solid phase transition (stoichiometric compound LiNaSO4). The experimental analysis carried out allowed to confirm the great potential of this system for TES application even if some discrepancies with the theoretical calculation have been observed experimentally (energy densities lower than expected). For the two compositions studied, 79/21 and 50/50, the enthalpies of reaction are 185 J/g and 160 J/g, respectively. The reactivity of the system was tested under different experimental conditions preparing materials with a different degree of nanocrystallization to favor the diffusion in the solid state, testing the reactivity of the materials under controlled atmosphere and under air, and performing preliminary durability analysis (cycling behavior up to 20 cycles) to test the stability and reversibility.


RSC Advances ◽  
2016 ◽  
Vol 6 (98) ◽  
pp. 96327-96333 ◽  
Author(s):  
Dong Fang ◽  
Xiaomin Cheng ◽  
Yuanyuan Li ◽  
Zheng Sun

Latent heat storage proves to be one of the most efficient ways of storing thermal energy.


2020 ◽  
Vol 5 (2) ◽  
Author(s):  
Olakunle F Isamotu ◽  
Nicholas A Musa ◽  
Joshua B Aluko ◽  
Maclawrence A Oriaifo

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


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