Display omitted
•Perforated fins are used in a finned shell and tube latent heat energy storage system.•Perforated fins outperform the solid fins by enhancing the natural convection.•30% enhancement ...in Nusselt number by applying perforated fins.•7% reduction in melting time by perforated fins instead of solid fins.
A key challenge in the deployment of practical latent heat energy storage systems employing phase change materials is the inherent low thermal conductivity of these materials. The present research is motivated by the need to intensify the buoyancy-driven convection flow in the phase change material to enhance the thermal performance of the system. In this paper, for the first time, the effect of applying perforated fins on the thermal performance enhancement of a vertical shell and tube latent heat energy storage heat exchanger is experimentally investigated and the results are compared with those of the unfinned and solid finned heat exchangers as the base cases. Lauric acid as the phase change material is placed in the shell side and the water is passed through the inner tube. The shells of the heat exchangers were made of transparent Plexiglas tubes to enable the visual comparison of the melting processes. The fins and tubes were made of copper. The melting process of phase change material is studied under different inlet water flow rates (0.5 and 1 l/min) and temperatures (55 and 65 °C). The experimental results showed that the time-averaged Nusselt number of the perforated finned heat exchanger is about 30% higher than that of the solid finned heat exchanger due to the minor hindering effect of the perforated fins on the development of the convection flows. Moreover, the total melting time of the perforated finned heat exchanger is about 7% lower than that of the solid finned heat exchanger.
We propose all‐dielectric metasurfaces that can be actively re‐configured using the phase‐change material Ge2Sb2Te5 (GST) alloy. With selectively controlled phase transitions on the composing GST ...elements, metasurfaces can be tailored to exhibit varied functionalities. Using phase‐change GST rod as the basic building block, we have modelled metamolecules with tunable optical response when phase change occurs on select constituent GST rods. Tunable gradient metasurfaces can be realized with variable supercell period consisting of different patterns of the GST rods in their amorphous and crystalline states. Simulation results indicate a range of functions can be delivered, including multilevel signal modulating, near‐field coupling of GST rods, and anomalous reflection angle controlling. This work opens up a new space in exploring active meta‐devices with broader applications that cannot be achieved in their passive counterparts with permanent properties once fabricated.
The all‐dielectric reconfigurable metasurfaces based on switchable phase‐change material Ge2Sb2Te5 with functional diversity for light modulation are shown. The tunability of EIT resonance on phase‐change metamolecule and the steering of gradient metasurface are demonstrated by selectively modifying the phase of selected constituent Ge2Sb2Te5 rods.
Display omitted
•Supercooling was suppressed by loading nanoparticles into the core.•The Effects of different types were compared.•The Effects of different mass fractions were compared.•The Effects ...of different particle sizes were compared.•The Effects of different coating methods were compared.
Due to the advantages of high thermal conductivity, high heat storage density per unit volume and large specific surface area, metal-based microencapsulated phase change material (MEPCM) has a broad application prospect in the field of medium/high-temperature heat storage. However, the problems of thermal expansion and large supercooling seriously restrict its development and application. Our previous research work showed that “double-layer coating, sacrificial inner layer” method can successfully solve the thermal expansion problem of metal-based MEPCM. Based on this method, we aim to further investigate the supercooling suppression of metal-based MEPCM by loading nanoparticles into the core material skillfully when sacrificing the inner layer. Phase change properties of three kinds of MEPCM loaded with different nanoparticles (nano-BN, nano-diamond, and nano-Fe) with the same concentration were compared. It was found that the supercooling suppression effect of nano-Fe was the best. Furthermore, supercooling suppression effect of nano-Fe with different concentrations was compared. The results demonstrated that nano-Fe with a concentration of 0.9% showed the best supercooling suppression effect. In addition, supercooling suppression effect of different particle sizes was compared. The results showed that the supercooling degree of MEPCM decreased by 41.5% and 5.6% when nano-Fe with a particle size of 50 nm and 100 nm was loaded, respectively, indicating that nano-Fe with the particle size of 50 nm is more effective than that of 100 nm. Finally, supercooling suppression effect of different coating methods was compared. The results showed that the supercooling suppression effect of “double-layer coating, sacrificial inner-layer” is much better than that of single-layer coating.
•The Al/Al2O3@Cu micro-encapsulated phase change materials (MEPCM) were prepared, and its performance was investigated.•The latent heat of Al/Al2O3@Cu MEPCM reaches 223.4 J/g.•The Al/Al2O3@Cu MEPCM ...can be used for high-temperature thermal energy storage at temperature over 660 °C.•The shell surface of Al/Al2O3@Cu particles is smooth and dense, after 10 melting–solidification cycles, the MEPCM particles maintain their integrity to prevent the leakage of liquid.
Phase change materials (PCMs) have the function of the high temperature thermal energy storage through the phase transition of Al alloys. The liquid alloys have certain liquidity and strong corrosivity. Therefore, general metals and alloys as container would hardly assure the long-term stability in high temperature. Therefore, the encapsulation of melt under the condition of high temperature is a necessary way to fabricate the practical materials. The study seeks to a new method to enhance the stability, high-temperature resistance, high-strength shell and leakage prevention by copper plating on the Al/Al2O3 composite surface. Firstly, the Al microspheres (20–40 µm) are treated by boiling treatment in water forms the AlOOH shell. The AlOOH shell was transformed into Al2O3 shell through heating at 550 °C. And then, the electroless copper plating is implemented to become the multilayered micro-encapsulated phase change material (MEPCM). The thermal durability, cross-sectional structure, surface morphology, and stability of the MEPCM are investigated. The latent heat of Al/Al2O3@Cu MEPCM reaches 223.4 J/g. The shell surface of Al/Al2O3@Cu particles are smooth and dense, after 10 melting–solidification cycles. Moreover, the MEPCM particles maintain their integrity to prevent the leakage of liquid which can be used for high-temperature thermal energy storage such as industrial waste heat recovery. The research also provides a method for the preparation of other heat storage materials, especially for the low-temperature metal-based PCMs.
With the development of economy, more and more problems related to energy have been paid more and more attentions. Phase change materials (PCMs) can store energy, which can better solve the problems ...of energy distribution and supply in some aspects. Because PCMs may be endothermic or exothermic at constant phase change temperature, they are favored in various industries. However, PCMs have a problem of poor thermal conductivity, which affects the heat transfer efficiency of the PCMs. This work reviews the methods to enhance thermal conductivity of PCMs. Thermal conductivity of PCMs is mainly enhanced through adding carbon-based materials and metal-based materials, etc. The PCMs with carbon-based materials and metal-based materials have better thermal characteristics and potential prospects of development and application. In addition, determining thermal conductivity methods, including determining thermal conductivity of PCMs theoretically and experimentally are are presented. Finally, the applications of the PCMs in some fields, such as solar energy utilization, building conservation, waste heat recovery and textile regulating temperature, are summarized and analyzed.
•The methods to improve thermal conductivity of phase change materials are summarized.•Some methods of determining thermal conductivity of phase change material are given.•The methods of measuring thermal conductivity of phase change material are presented.•The applications of phase change material in some fields are summarized and analyzed.
•Effect of using porous TCEs with gradient pore structures are discussed.•Gradient porous TCE can improve thermal performance of PCM energy storage systems.•Various heating modes are studied and ...superiority of gradient porosity is revealed.•Direction of gradient porosity and PPI affect conductivity and natural convection.•PCM melting and circulations are discussed in detail for gradient foam structures.
In this work, a comprehensive analysis is presented on utilizing non-homogeneous porous metal foams as thermal conductivity enhancers (TCEs) in energy storage systems and heat sinks working with phase change materials (PCMs). The transient phenomena inside the PCM-based systems with TCEs of gradient pore structure is numerically investigated and compared to the conventional uniform porous TCEs. The metallic foam is assumed to be made of copper, and paraffin is employed as the phase change material. Simulations are performed using finite-volume discretization, and Darcy-Brinkman-Forchheimer model is employed to represent the porous medium with variable properties. First, the effect of a positive and negative gradient porous structure in various spatial directions is discussed in detail and thermal response of the energy storage system to different thermal loads is compared to the case with uniform structure. The results show that gradient porous TCEs can be designed to improve the thermal performance of PCMs, and provide more uniform melting profile and heat transfer distribution throughout the system. The improvement has been shown for various heating configurations and at different melting stages. A general melting pattern is found for the left-heated layouts while comparatively, the bottom-heated layouts have more distinct melting profile. Also, the cases with lower porosity at the heat source have relatively higher melting rate at the beginning but a lower one at the final melting stages. Afterwards, variations of the porosity parameters such as average porosity, porosity change rate, and pore density in the gradient porous TCEs is studied for selected designs under different heat load conditions. The results show that when these porous foam features are changed, the thermal response and increase or decrease of the melting rate for the various structures is different. The differences in the melting and natural convection behavior is thoroughly discussed. At the final stage of this work, the thermal performance of the uniform and gradient porous structures is evaluated and compared at different widths and heights of the energy storage system. The results show that depending on the heat source location and the direction of the gradient foam with respect to the gravity, the improvement is more eminent when the size of the enclosure changes at certain directions. When increasing the height of the enclosure, a positive foam gradient in y direction has a better melting for the left-heated layouts while a positive foam gradient in x direction is superior for the bottom-heated layouts.
Phase change material (PCM) technology is an interesting method for battery thermal management, while the cooling behavior and cooling efficiency of PCM on prismatic lithium-ion batteries are ...unclear. In this work, a series of experiments are conducted to systematically investigate the cooling efficiency of PCM and the several detailed factors on the thermal management performance, such as the structure, phase change temperature and thickness of PCM. The results show that the PCM structure (sides of the battery surround by PCM) has an excellent heat dissipation efficiency at high discharge rate of 2C. Decreasing the phase change temperature is beneficial to enhance the cooling performance. Moreover, increasing the thickness of PCM enhances the cool performance, but the heat dissipation efficiency will decrease once the thickness exceeds the value of 25 mm, hence the selection of the PCM thickness is variable based on the heat dissipation capability and cooling efficiency. Furthermore, by investigating the cooling behavior of PCM during the cycle test, it is found that the PCM structure with 25 mm thickness can keep the maximum temperature of the battery under 55 °C in dynamic cycling. This work can provide experimental references for the thermal management system of prismatic batteries.
•The thermal performance of large format lithium-ion battery during charge and discharge stages was experimentally studied.•Quantifying the heat dissipation capacity and heat dissipation efficiency of PCM in the battery thermal management.•The effects of phase change temperature and thickness of PCM on the thermal management system were analyzed.•The PCM module with 25 mm thickness has an excellent cooling performance in dynamic cycling.
•Influences of the incorporation of nano particles in PCMs are reviewed.•Main advantages of nano incorporated PCMs in energy systems are lower specific heat and improved thermal conductivity.•Using ...nano-incorporated PCMs in addition to fins significantly accelerates charging/discharging rates.•In addition to thermal storage, nano-incorporated PCMs are attractive alternatives for current cool storage units.
Phase Change Materials (PCMs) have being used in different solar energy systems for thermal energy storage and performance enhancement. Improving heat transfer from PCMs leads to reductions in charge and discharge durations, which makes them more favorable as storage units. Dispersion of conductive solid materials with nano dimensions is a practical approach to enhance their thermal features. Several nano-sized materials have been added to PCMs to improve their heat/cool storage abilities. The studies in this field reveal that employing nanotechnology is an efficient method for heat transfer improvement. In the current article, studies concerning applications of nanotechnology in PCMs are reviewed. According to the results, employing nanotechnology can noticeably enhance the heat transfer rate, which results in a reduction of charge and discharge times of the storage units equipped with the PCMs. The enhancement in the melting process of nano PCMs, which indicates the storage performance, depends on several factors such as concentration and kind of solid nano-sized particles, type of base PCM and the parameters related to operating conditions such as Rayleigh and Darcy numbers. The improvement in thermal performance due to nano PCMs is mainly attributable to the increased thermal conductivity and decrease in latent heat of fusion, which accelerates the melting/solidification processes.
•A kind of composite phase change material board (PCMB) is prepared and tested.•PCMB presents a large thermal storage capacity and enhanced thermal conductivity.•PCMB displays much better cooling ...effect in comparison to natural air cooling.•PCMB presents different cooling characteristics in comparison to ribbed radiator.
A kind of phase change material board (PCMB) was prepared for use in the thermal management of electronics, with paraffin and expanded graphite as the phase change material and matrix, respectively. The as-prepared PCMB presented a large thermal storage capacity of 141.74J/g and enhanced thermal conductivity of 7.654W/(mK). As a result, PCMB displayed much better cooling effect in comparison to natural air cooling, i.e., much lower heating rate and better uniformity of temperature distribution. On the other hand, compared with ribbed radiator technology, PCMB also presented different cooling characteristics, demonstrating that they were suitable for different practical application.
A double passes solar air collector–coupled modified solar still, with Phase Change Material (PCM), have been experimentally investigated to enhance the freshwater productivity. The influence of the ...injected hot air on the performance of a modified still, with PCM, is investigated. A comparison between a modified still, with both PCM and hot air injection, and the conventional still is carried out to evaluate the enhancement in the freshwater productivity. The experiments were carried out under the same atmospheric conditions. The experimental results show that, the freshwater productivity approximately reached 9.36 (L/m2day) for the double passes solar air collector–coupled modified solar still, with PCM, while its value is recorded 4.5 (L/m2day) for the conventional still. The freshwater productivity of the double passes solar air collector–coupled modified solar still with PCM is 108% higher than that of the conventional still on average. This percentage is obtained during the period from June to July 2015 under the Egyptian climatic conditions.
•A solar air collector-coupled modified solar still with phase change material have been investigated•A comparison between modified still with and conventional still is carried out•The augmentation of freshwater productivity for modified still reached 109 % compared to conventional still
PDF
