Thermal energy storage (TES) systems using phase change material (PCM) have been recognized as one of the most advanced energy technologies in enhancing the energy efficiency and sustainability of ...buildings. Now the research is focus on suitable method to incorporate PCMs with building. There are several methods to use phase change materials (PCMs) in thermal energy storage (TES) for different applications. Microencapsulation is one of the well known and advanced technologies for better utilization of PCMs with building parts, such as, wall, roof and floor besides, within the building materials. Phase change materials based microencapsulation for latent heat thermal storage (LHTS) systems for building application offers a challenging option to be employed as effective thermal energy storage and a retrieval device. Since the particular interest in using microencapsulation PCMs for concrete and wall/wallboards, the specific research efforts on both subjects are reviewed separately. This paper presents an overview of the previous research work on microencapsulation technology for thermal energy storage incorporating the phase change materials (PCMs) in the building applications, along with few useful conclusive remarks concluded from the available literature.
•Experimental investigation of phase change material in thermoelectric generators.•Phase change material stores solar heat for later use.•Thermoelectric generator model and paraffin type affected ...stored energy capacity.•TEG model and paraffin type affected phase change material melting time.•Thermoelectric generator harvested electricity during charging and discharging.
In this present study, a phase change material (PCM) based thermal energy storage unit (TESU) integrated with thermoelectric generators (TEGs) was experimentally investigated under artificial solar radiation. Within the scope of the experiments, a TESU with the dimensions of 15x15x5 cm was designed by assembling nine TEGs connected in series on the TESU. In the design, two types of paraffin based PCM with different thermophysical properties values as PCM in TESU and two models of TEGs with different power were used. Four different TEG/TESU designs with different parameters were made, namely TEC1-12706/P1, TEC1-12706/P2, TEC1-12710/P1, and TEC1-127010/P2. Charge-discharge processes of each design were investigated under radiation intensities of 800, 1000, and 1200 W/m2. According to the results of the experiments, it was observed that as the power of the TEG used increased, the melting time of the paraffin was shortened, and the energy conversion efficiency (ECE) and the thermal energy storage efficiency (TESE) increased. It was determined that the maximum power obtained from the designs with TESU was approximately 11% higher than that without TESU. The result showed that more efficient TEG systems would be obtained by making the temperature of the cold surface of TEGs more stable with PCM. In addition, it was determined that the melting time decreased and the TESE and ECE increased with the increment of the radiation intensity. The shortest melting time of 135 minutes, the highest TESE of 80.72% and the highest ECE of 2.32% were obtained from the TEC1-12710/P2 design under 1200 W/m2 radiation. The longest melting time of 240 minutes, the lowest TESE of 64.62% and the lowest ECE of 2.04% were obtained from the TEC1-12706/P1 design under 800 W/m2 radiation.
This study regards the evaluation of the performance of a thermally stratified tank as an intermediate combi-storage tank for a solar-driven residential thermal system coupled to a seasonal energy ...storage system. In such applications, the efficient operation of this intermediate tank is crucial to the enhanced exploitation of the harvested solar energy and the minimization of heat losses. In this perspective, the development of a dedicated model in TRNSYS software and its validation with experimental results are investigated. With respect to the simulation model’s discretization, it was found that beyond 60 nodes, the benefits to the model’s accuracy are almost negligible. Comparing the experimental data with the simulation’s results, the predicted temperature profile converges accurately to the measured values under steady-state conditions (threshold stabilization period of 1000 s after charging/discharging has occurred). However, the response of the model deviates considerably under transient conditions due to the lack of detailed inertia modeling of both the tank and the rest of the system components. Conclusively, the developed 1D simulation model is adequate for on- and off-design models where transient phenomena are of reduced importance, whereas for dynamic and semi-dynamic simulations, more detailed models are needed.
•PCMs integrated building envelope and equipment in 2004∼2017 are reviewed.•Melting temperature range of PCMs used for envelope is 10∼39°C.•Melting temperature range of PCMs used for equipment is ...−15.4∼77°C.•PCMs’ positive effects on energy saving and thermal comfort are demonstrated.•The existing gaps in the research works are identified and classified as 5 aspects.
Confronted with the crises of the growing resource shortages and continued deterioration of the environment, building energy performance improvement using phase change materials has received much attention in recent years. This review work provides an update on recent developments, 2004∼2017, in phase change materials used to optimize building envelope and equipment. Firstly, a review of building envelope optimization methods by integrating surrounding wall, roof, and floor with phase change materials, is given. This is followed by reporting articles on building equipment optimized with phase change materials to reduce regular energy consumption. Series of air cooling, heating, and ventilation systems coupled with thermal energy storage were comparatively investigated. Finally, the existing gaps in the research works on energy performance improvement with phase change materials were identified, and recommendations offered as authors’ viewpoints in 5 aspects. It was also found that the phase change temperature range of PCMs used was changed from 10∼39°C for envelope to −15.4∼77°C for equipment. We believe this comprehensive review might provide an overview of the analytical tools for scholars, engineers, developers, and policy designers, and shed new light on the designing and performance optimization for PCMs used in building envelope and equipment.
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•This study deals with liquid metals, molten salts and other heat transfer fluids.•Molten salts show advantages in operating conditions up to 800°C.•Temperature range, viscosity, ...thermal conductivity and corrosion etc. are discussed.
There is a strong motivation to explore the possibility of harnessing solar thermal energy around the world, especially in locations with temperate weather. This review discusses the current status of heat transfer fluid, which is one of the critical components for storing and transferring thermal energy in concentrating solar power systems. Various types of heat transfer fluids including air, water/steam, thermal oils, organic fluids, molten-salts and liquid metals are reviewed in detail, particularly regarding the melting temperature, thermal stability limit and corrosion issues. Stainless steels and nickel based alloys are the typical piping and container materials for heat transfer fluids. Stability of the stainless steels and alloys while in contact with heat transfer fluids is very important for the longevity of concentrating solar power systems. Corrosion properties of stainless steels and nickel based alloys in different heat transfer fluids are discussed in terms of corrosion rates.
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•Three-dimensional porous diamond foam with high quality was fabricated.•Paraffin-based phase change materials incorporated with diamond foam were synthesized.•Thermal conductivity of ...the composite was significantly enhanced.•The enhancement was attributed to the interconnected diamond networks with high thermal conductivity.•Improved shape stability and good thermal reliability were achieved.
For thermal energy storage applications using phase change materials (PCMs), the power capacity is often limited by the low thermal conductivity (λPCM). Here, a three-dimensional (3D) diamond foam (DF) is proposed by template-directed chemical vapor deposition (CVD) on Cr-modified Cu foam as highly conductive filler for paraffin-based PCM. Results showed the foam substrate was completely covered by continuous diamond films with high quality. And it showed a faster thermal response than that of Cu foam (CF) and Cu disc, while only a little slower than that of free-standing diamond disc with the same thickness. The incorporation of interconnected diamond foam with the diamond volume fraction of only 1.3% in the composite phase change material represented a great thermal conductivity enhancement over the pure paraffin, CF/paraffin and diamond particles reinforced paraffin by a factor of 25.8, 1.62 and 13.88, respectively. The great enhancement of the thermal conductive property was mainly attributed to interconnected diamond networks with high thermal conductivity, which effectively reduced the phonon-phonon and phonon-boundary scatterings. Besides, the DF/paraffin composite PCM exhibited an improved shape stability and a fast heat charging rate with the latent heat of 124.7 J/g. The marriage of the excellent properties of diamond and the inherent advantages of the 3D interconnected structure makes the diamond foams potential components or act as reinforcements in the field of high-efficiency heat dissipation and thermal energy storage.
•The ratios of eutectic salt (NaCl–KCl–Na2CO3) were predicted by means of thermodynamic calculations.•Doping of Al2O3 nanoparticles enhances the thermal properties of eutectic salts.•Doping of ...2.0 wt% Al2O3 nanoparticles increased TES densities by 9.91%.•Nanoparticle doping shortens melting time by 82 s.
With the introduction of the Brayton cycle technology, molten salts have become one of the most promising thermal storage materials in thermal energy storage (TES) systems. In this study, a novel eutectic salt (ES) NaCl–KCl–Na2CO3 was used as the base salt and Al2O3 nanoparticles (NPs) as additives to prepare Nano-ES. Both thermal analysis and molecular dynamics results showed that the doping of Al2O3 NPs improved the thermophysical properties of the ES. In particular, the TES density and liquid-state thermal conductivity of the ES increased by 11.60 % and 28.62 %, respectively, when the content of NPs was 2.0 wt%. The improvement in thermophysical properties was attributed to the NPs-induced change in the microstructure of the ES. However, the doping of NPs led to inevitable increase in the viscosity of the ES, which directly affected the strength of natural convection. This study further analyzed the melting process of ES and Nano-ES in shell-tube TES system, and the results showed that the melting rate of TES materials was affected by natural convection and thermal conductivity. The ES with lower viscosity and thermal conductivity exhibited a melting rate close to that of Nano-ES at 420–540 s stage. The viscosity of the TES materials should not be neglected during the application of TES systems. This study provides an important guiding significance for the selection of molten salts and additives for high-temperature TES systems.
•Metal foam with gradient in porosity markedly affected the melting process than pore density.•Metal foam with positive gradient in pore parameters showed a better temperature uniformity.•An optimal ...gradient porosity (0.89–0.95–0.98) could reduce the full melting time by 21.1%.•Positive gradient design exhibited a prospective capacity for enhancing melting heat transfer.
In this paper, a novel latent heat thermal energy storage unit filled by metal foams with gradient in pore parameters was proposed to enhance thermal energy storage performance. Two kinds of gradients, namely positive and negative gradients, in porosity and pore density for metal foams were designed. Physical and numerical models were established for this problem to predict the melting front evolution, temperature and velocity field during the melting process. An experimental test rig was built and measurements on temperature variation in paraffin/metal foam composite were conducted to validate the numerical model, achieving good agreement. The temperature variations and evolution of melting front were explored and recorded. The numerical results demonstrated that the positive gradient in porosity can provide the better heat transfer enhancement than the uniform and negative gradient cases. A 17.9% reduction in full melting time can be achieved with the positive gradient design of porosity and simultaneously a better temperature uniformity was also obtained in comparison with the other arrangements. Improving the arrangement of pore density contributed little to the melting process but the temperature uniformity for the case with positive gradient in pores density increased by 9.1% compared to the uniform arrangement. An optimization recommended on a gradient in porosity of 0.89–0.95–0.98 to further reduce the full melting time by 21.1%.
•A 3-D numerical model of the square LHS unit melting process is established.•The melting properties of four different structures are quantitatively compared.•The melting time, temperature uniformity ...and total heat storage are discussed.•The effect of strengthening method is studied in depth by dynamic temperature study.
The low thermal conductivity of phase change materials limits the large-scale application of latent heat storage technology. It is meaningful to improve the thermal conductivity of phase change materials by corresponding means. In order to improve the performance of latent heat storage device, this paper takes square latent heat storage device as the research object, and uses fin and foam metal to enhance its melting performance. A 3-D numerical model is established and verified by visualization experiment. The quantitative comparison of melting properties of four different structures (pure paraffin, fin, metal foam, fin-metal foam) is presented. The results show that compared with pure paraffin structure, the complete melting time of phase change materials corresponding to fin, metal foam, and fin-metal foam structure is reduced by 47.48%, 79.53%, and 83.68%, respectively. The temperature uniformity increased by 28.97%, 79.37%, and 91.12%, and the total heat storage decreased by 6.0%, 4.6%, and 11.64%, respectively. It shows that the addition of fin and foam metal is beneficial to improve the melting performance and the overall temperature uniformity of the device, but it has a negative effect on total heat storage. Dynamic temperature studies were conducted to further explore the effect of fins and metal foam on the internal melting process compared with pure paraffin structure.
