MePCMs (microencapsulated phase change materials) with covalently bonded SiO sub(2)/polymer hybrid as shell were fabricated via Pickering emulsion polymerization stabilized solely by ...organically-modified SiO sub(2) particles. Morphology and core-shell structure of these microcapsules were observed by scanning electron microscopy (SEM). Thermal properties of microencapsulated 1-dodecanol were determined using DSC (differential scanning calorimetry) and TGA (thermal gravimetric analysis). The results indicate that mass ratio of St (styrene)/DVB (divinylbenzene)fdodecanol has great effect on the morphology, inner structure, microencapsulation efficiency and durability of resultant MePCMs. When ratio of St/DVB/dodecanol was 5/1/12, dodecanol content of as much as 62.8% is obtained and the utility efficiency of dodecanol reaches 9.4.2%. The prepared MePCMs present good durability and thermal reliability. 2.2% of core material leached away the microcapsule after suspended in water for 10 days and 5.8% of core material leached after 2000 accelerated thermal cycling. Our study demonstrated that Pickering emulsion polymerization is a simple and robust method for the preparation of MePCMs with polymer-inorganic hybrids as shell.
Effects of oxidation degree of GO on the structure and performance of shape-stabilized PCMs for an effective photo-to-thermal energy conversion and storage are examined.
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•GAs with ...diverse structure are fabricated by tuning the oxidation degree of GO.•The composite PCMs exhibits excellent shape-stability at high temperature.•The structure of GA plays a significant role in the shape-stability of composite PCMs.•Efficient light-to-thermal energy conversion and storage are realized.
Polyethylene glycol (PEG)/graphene oxide aerogel (GA) composite phase change materials (PCMs) were prepared by introducing PEG into GAs from graphene oxide (GO) with different oxidation degree via vacuum impregnation. The structures of GAs were tuned by the oxidation levels of GO. A series of characterizations were used to analyze the chemical structure of GOs, including X-ray diffraction (XRD), Fourier transform infrared spectrum (FTIR), X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy analysis. Structural analyses confirmed that the oxygenated functional groups increased and the hydroxyl groups were transformed into carboxyl and epoxy groups with increasing oxidation level. In addition, the graphitic nature of GO decreased while the sp3 domains of GOs increased owing to the disruption of the graphitic stacking order. Morphology analysis showed that the breakage of graphene sheet became more serious with the oxidation level increasing. When GAs prepared with GOs of higher oxidation levels were used, the composite PCMs showed excellent shape-stability during phase change and excellent thermal repeatability. The change of dimension for PGA6-40 heated from 35°C to 150°C was negligible under the load of a constant force (7N). Efficient photo-to-thermal energy conversion and storage was realized in the composite PCMs.
•Numerical and experimental study were performed to provide insight into the thermal behavior.•The comparative analyses of sensible heat storage and phase change thermal storage were provided.•The ...maximum temperature difference of the SHM appeared in the middle of the thermocline.•Total storage charging time was reduced with the decrease of the melting point and latent heat.
Thermal energy storage is an important subsystem of a solar thermal power station. Compared with the two-tank storage system, the packed bed storage system uses a single tank to store thermal energy temporarily and release it when the energy is needed. The temperature distribution in the packed bed is generally in the form of the thermocline. This study analyzed a thermocline storage system packed with sensible heat material and phase change material. These materials were characterized separately in terms of temperature difference, outlet temperature profile, total energy storage, and charging time. Results demonstrated the presence of a maximum temperature difference in the middle of the thermocline. The maximum value of the temperature difference decreased following an increase in the charging time. The density and conductivity of the sensible material and the inlet velocity of the fluid considerably affected the temperature difference. In the phase-change thermal storage system, the temperature difference between the material and the fluid exhibited two peaks, wherein the first peak was higher than the second peak. The total storage charging time and storage energy increased following an increase in latent heat. The total storage charging time was reduced following a decrease in melting point, although the final thermal energy storage remained the same.
Non-volatile phase-change materials with large optical contrast are essential for future tunable nanophotonic applications. Antimony trisulfide (Sb2S3) has recently gained popularity in this field ...due to its low absorption in the visible spectral region. Although several Sb2S3 deposition techniques have been reported in the literature, none of them was optimized with respect to stoichiometry, lowest possible absorption, and large refractive index contrast (Δn) upon the phase change. Here we present a comprehensive multi-parameter optimization of pulsed laser deposition of Sb2S3 towards this end. We correlate the specific deposition with the resulting compositional and optical properties and report parameters leading to films with extraordinary qualities (Δn = 1.2 at 633 nm). Additionally, we suggest crystal orientations and vibrational modes associated with the largest change in the refractive index and propose them as useful large-scale indicators of the Sb2S3 switching contrast.
•Beam splitting nano-enhanced phase change materials were studied in a PV/T system.•A detailed optical model was developed using Mie theory and Rayleigh approximation.•A parametric study was ...performed to determine the optimum conditions.•The proposed system successfully filtered the radiation, and stored thermal energy.•Maximum exergetic efficiency of 24% was achieved for a concentration ratio of 30.
Photovoltaic cells can convert incoming sunlight within their responsive wavelength range into electricity. Unfortunately, the majority of the incident radiation is reflected, absorbed directly as heat, or indirectly converted to heat due to internal losses (i.e., ≥ 52.9%, even world-record efficiency cells). In concentrated photovoltaic systems, this added heat can further degrade the electrical conversion efficiency of the cells if it is not removed, resulting from an elevated operating temperature. Spectral splitters and absorptive filters can remove the unused portion of the solar spectrum before it is converted to heat in the photovoltaic cells and harvest this energy for active use in thermal applications. In this paper, an innovative concentrated photovoltaic/thermal system that utilizes a layered design containing an optical fluid and a phase change material was investigated as a new alternative absorptive filter. Five possible configurations of this filter were compared from energy, exergy, and energy storage perspectives. These layers consist of a phase change material (dotriacontane, a paraffin) layer and fluid channel layers (a glycerol fluid) with suspended Ag and/or Au nanoparticles. The optical properties of the nanofluid and the nano-enhanced phase change material (NEPCM) were modeled using Mie and Rayleigh scattering theories. The comparison showed that the configuration containing the nanofluid channel at the top of the nano-enhanced phase change material performs well in all aspects of energy, exergy, and energy storage. A parametric study was conducted to determine the effects of nanoparticles volume fraction, concentration ratio, mass flow rate, nanofluid thickness and phase change material thickness on PV/T system performance with this filter configuration. It was found that volume fractions lower than 0.3 × 10−5 and 0.2 × 10−5 for Ag and Au, respectively, provided the best system performance for the assumed geometric and operational conditions. At an optimal mass flow of 0.005 kg s−1 for the nanofluid, this design achieved a maximum exergetic efficiency of 24% for a concentration ratio of 30. The results also revealed that the nanofluid-NEPCM filter is not suitable for concentration ratios of less than 10. Overall, this study finds that nanofluid-NEPCM-based spectral splitter, in addition to successfully filtering radiation, can store energy efficiently.
Water-nano encapsulated phase change material (water-NEPCM) is a promising, new coolant made from PCM nano capsules dispersed in water. In this study, a water-NEPCM battery thermal management system ...(BTMS) for an 18650 Li-ion battery pack is studied using momentum, electrochemical and energy equations. The results show that water-NEPCM can lower the battery cell's average and maximum temperatures up to 34% and 51% respectively in comparison with water systems. Moreover, when water-NEPCM is used, up to 78% more temperature uniformity can be achieved. Furthermore, the electrochemical analysis shows that water-NEPCM increases Li-ion concentration differences in the battery cells by 6% and 3.31% for solid and liquid phases respectively. Also, it is revealed that water-NEPCM causes reduction in batteries voltage up to 2.74 mV. Performance evaluation criterion (PEC) results expresses that when both the better thermal performance and energy consumption are desired, it is necessary to adjust the coolant flow rate in a specific range and using the battery systems with high heat production rates is recommended. According to the results, the water-NEPCM BTMS can be supposed as a novel promising system alternative to the conventional water-cooled ones because more reduction and uniformity can be achieved for the temperature distribution.
•A water-NEPCM 18650 Li-ion battery thermal management system is studied.•Water-NEPCM can propose good temperature reduction and uniformity.•The performance of water-NEPCM is highly dependent on the battery usage situation.•Water-NEPCM can be used with better PEC relative to pure water in some conditions.
The NaCl–KCl–NaF eutectic salt was designed and developed by Pandat software and experiment. Thermal transport and storage performances were determined by experimental measurements. The melting point ...of the NaCl–KCl–NaF eutectic salt is 604.1 °C and the fusion enthalpy is up to 398.4 J/g. The thermal conductivity average value was 1.037 ± 0.074 W/m−1·°C−1. The weight loss of NaCl–KCl–NaF eutectic salt is still less than 6.0% even up to 900 °C and the eutectic salt have very excellent thermal stability. The NaCl–KCl–NaF eutectic salt with high latent and suitable temperature have good economy performance even with expensive individual salt of NaF. The NaCl–KCl–NaF eutectic salt with suitable phase change temperature, low cost, high latent heat, excellent stability and good economy performance can be a candidate phase change material for next generation concentrated solar power with supercritical CO2 cycles.
•NaCl–KCl–NaF eutectic salts were designed and developed by Pandat and experiment.•Tm of the eutectic salts is 604.1 °C and the fusion enthalpy is up to 398.4 J/g.•The eutectic salts have very excellent thermal stability.•The eutectic salts with high latent & suitable temperature have good economy performance.
•Metallic PCMs demonstrated as a fast thermal transient mitigation solution (<20ms).•Demonstrated metal PCM in direct contact with high power device and integrated RTD.•Two metallic PCMs compared ...with organics paraffin PCMs and baseline gel encapsulant.•Metallics show 62°C (60%) lower temperature rise than organics, 78°C (66%) than gel.
The military has various high rate transient pulse applications which create unique thermal management challenges due to their high heat flux and short pulse duration. Phase change materials (PCMs) have been studied due to their ability to absorb thermal energy with minimal temperature increase. This work investigates the performance of metallic PCMs (Fields’ metal (32.5Bi/51In/16.5Sn wt%) and 49Bi/18Pb/12Sn/21In wt%) acting as an integrated thermal buffer for high power 19ms pulses. Two commercially available organic PCMs (PureTemp 29® and PureTemp 58®) and a dielectric gel (Sylgard 527®) were used for comparison. The studied materials were deposited directly in contact with the heat-dissipating surface of a custom micro-fabricated heater chip with an embedded resistance temperature detector (RTD) for in-situ temperature measurement. PCMs were subjected to 19ms pulses and a maximum heat flux of 338W/cm2 (relative to heat source area). The Bi/Pb/Sn/In PCM was able to reduce temperature rise during the pulse by 60°C (63%) for 120W and 81°C (68%) for 160W using the dielectric gel as baseline. In comparison the best performing organic PCM, PureTemp58, only reduced temperature rise by 16°C (17%) and 17°C (14%) for 120W and 160W, respectively. This supports previous assertions in the literature that metallic PCMs can be an enabling thermal protection technology for high rate transient applications.
The GeTe phase-change RF switch with Ag conductive filament (CF) as heater is fabricated. The Ag CF as heater can effectively reduce the energy consumption of the switch. In particular, the set ...energy consumption is as low as 19.2 nJ to set the switch. In durability test, the resistance ratio exceeds three orders of magnitude and remains almost constant over 1000 cycles. The insertion loss of the phase-change RF switch based on GeTe is less than 0.8 dB and the isolation is greater than 20 dB up to 67 GHz. The cut-off frequency of the switch is as high as 15 THz. This work demonstrates that the modulated CF can be used as the heater for phase change material (PCM), providing a new micro directly heated structure for low energy consumption phase-change RF switch.
In order to augment the efficiency and distillate yield in the concentrator-coupled hemispherical basin solar still, a phase change material (PCM) was added. Two modes of operation have been studied ...experimentally, (1) single-slope solar still without the PCM effect, and (2) single-slope solar still with the PCM effect. The temperature of water (Tw), temperature of PCM (TPCM), air temperature (Tair), inner cover temperature (Tic) and outer cover temperature (Toc) were measured. Experimental results indicate that the effect of thermal storage in the concentrator-coupled hemispherical basin solar still increases the productivity by 26%. It was concluded that the productivity greatly increased due to the still integrated with PCM.
► We optimized the augmentation of condense by enhanced desalination methodology. ► Compound conical concentrator has been integrated with solar still. ► We measured ambient together with solar radiation intensity.
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