•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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•Novel PCMs with acoustic-thermal energy conversion and management ability were developed.•The composites present exceptional sonic wave absorption and heat energy conversion ...properties.•The composites exhibit high phase change enthalpies (173.7 J/g).•The composites show enhanced thermal conductivities and shape-stabilities.
Sonic energy can be converted into thermal energy by ultrasonic thermal effect, which has significant application value in the fields of denoising and minimally invasive thermotherapy. Acoustic thermal conversion and thermal energy management capacities need to effectively improved during the process of acoustic-thermal utilization. Herein, we report novel PEG/Fe3O4-GO form-stable phase change materials (PCMs) with efficient sound wave absorption, acoustic-thermal conversion and thermal management capability. The PCMs are prepared by in-situ encapsulating polyethylene glycol (PEG) into graphene oxide (GO) network functionalized with Fe3O4 nanoparticles. The unique construction of three-dimensional (3D) network structure not only improve thermal conductive performance but also enhance sound absorption ability effectively. Moreover, the acoustic-thermal conversion is further enhanced through the vibration heat production of Fe3O4 nanoparticles. As a result, the form-stable composites exhibit superior energy storage density (173.7 J/g) and acoustic-thermal conversion performance. Thereby opening up a broad application prospect in the field of acoustic to heat energy conversion and storage.
•For ventilation pre-cooling application, the room inlet air temperature is by average 1.4 °C lower for 7 h during the daytime compared to the normal VW.•In ventilation pre-heating application, the ...PCM increases the inlet air temperature of the VW by 2.0 °C for 12 h.•Buildings in a climate with high daily outdoor air temperature differences can benefit more from the PCMVW in ventilation pre-cooling application.•In ventilation pre-heating application, the buildings in climate with higher solar radiation levels has a higher energy performance.•The VW self-cooling application is effective to decrease the overheating of the room.
This paper presents a phase change material enhanced ventilated window (PCMVW) for both ventilation pre-cooling and pre-heating purposes. The PCM heat exchanger is used as a heat sink in the ventilation pre-cooling application and thermal energy storage in the ventilation pre-heating application. The paper presents a night cooling experiment and a solar energy storage experiment in order to investigate the thermal and energy performance of the PCMVW, and a ventilated window (VW) self-cooling experiment for overheating protection. Two VWs were tested in the façade lab in Aalborg (Denmark), and one of them is with PCM heat exchanger. The two windows were equipped with the same outdoor conditions and ventilation airflow. The experimental results show that for ventilation pre-cooling application with the PCM heat exchanger, the room inlet air temperature is by average 1.4 °C lower for 7 h during the daytime compared to the normal VW. The average energy saving is 0.7 MJ/day compared to a normal VW. The PCMVW cooling capacity is limited without advanced blinds control and system operation control. In ventilation pre-heating application, the PCM increases the inlet air temperature of the VW by 2.0 °C for 12 h. The average energy saving is 1.6 MJ/day compared to a normal VW. Buildings in a climate with high outdoor air temperature differences can benefit more from the PCMVW in ventilation pre-cooling application, but the pre-cooling ability is limited. While in ventilation pre-heating application the buildings in the climate with higher solar radiation levels has a higher energy performance. Moreover, the VW self-cooling application is more effective to decrease the overheating of the room than VW without self-cooling.
•A hierarchical structured hypercrosslinked polymer/expanded graphite composite was developed for PCM shape-stabilization.•Up to 89.4% encapsulation rate with thermal conductivity of 3.7 W/m•K.•Up to ...93% light-thermal efficiency was obtained using the hierarchical structured PCM composite.
Thermal energy storage and release is of great interest in solving mismatch between energy supply and demand. Latent heat capacity and thermal conductivity are the two main factors needed to be considered for practical applications of shape-stabilization phase change materials (PCMs). Herein, a hierarchical hypercrosslinked polymer (HCP)/expanded graphite (EG) composite, could fulfill both superior high specific surface area and thermal conductivity requirements, was synthesized via an in-situ growth protocol in the pore of expanded graphite. It was suggested that a synergistic working mechanism existed between EG and HCP, where EG acted as a macro pore system for the inhibition of HCP aggregation, which could thus enable a better encapsulation rate of PCM in HCP; while HCP played a role for the highly efficient encapsulation owing to its high specific surface area. Hierarchical structured HCP/EG composite exhibits promising performance when used as a PCM supporting material that the encapsulation rate of the composite could reach to 89.4% without observation of any leakage, and the thermal conductivity is up to 3.7 W•m−1•K−1. Additionally, the prepared PCM composites display a superior heat energy storage and light-to-thermal conversion performance over pure paraffin, indicating its great potential to be used in thermal energy storage.
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