Thermal energy storage technologies based on phase‐change materials (PCMs) have received tremendous attention in recent years. These materials are capable of reversibly storing large amounts of ...thermal energy during the isothermal phase transition and offer enormous potential in the development of state‐of‐the‐art renewable energy infrastructure. Thermal conductivity plays a vital role in regulating the thermal charging and discharging rate of PCMs and improving the heat‐utilization efficiency. The strategies for tuning the thermal conductivity of PCMs and their potential energy applications, such as thermal energy harvesting and storage, thermal management of batteries, thermal diodes, and other forms of energy utilization, are summarized systematically. Furthermore, a research perspective is given to highlight emerging research directions of engineering advanced functional PCMs for energy applications.
A comprehensive review regarding the tuning of the thermal conductivity of phase change composites for thermal energy conversion, storage, and utilization is provided, which gives an insightful understanding of the thermal energy storage and conversion processes. The aim is to stimulate potential emerging applications of phase change materials.
Image-level weakly supervised semantic segmentation is a challenging problem that has been deeply studied in recent years. Most of advanced solutions exploit class activation map (CAM). However, CAMs ...can hardly serve as the object mask due to the gap between full and weak supervisions. In this paper, we propose a self-supervised equivariant attention mechanism (SEAM) to discover additional supervision and narrow the gap. Our method is based on the observation that equivariance is an implicit constraint in fully supervised semantic segmentation, whose pixel-level labels take the same spatial transformation as the input images during data augmentation. However, this constraint is lost on the CAMs trained by image-level supervision. Therefore, we propose consistency regularization on predicted CAMs from various transformed images to provide self-supervision for network learning. Moreover, we propose a pixel correlation module (PCM), which exploits context appearance information and refines the prediction of current pixel by its similar neighbors, leading to further improvement on CAMs consistency. Extensive experiments on PASCAL VOC 2012 dataset demonstrate our method outperforms state-of-the-art methods using the same level of supervision. The code is released online.
•A heat pipe assisted phase change material based battery thermal management system is proposed.•The proposed system is compact and efficient from a view of practical application.•Cycling conditions ...are experimentally simulated for practical working environment.•The proposed system presents better thermal performance in comparison to other systems.•Combining forced air convection with heat pipe further enhances the cooling effect.
In this paper, a heat pipe-assisted phase change material (PCM) based battery thermal management (BTM) system is designed to fulfill the comprehensive energy utilization for electric vehicles and hybrid electric vehicles. Combining the large heat storage capacity of the PCM with the excellent cooling effect of heat pipe, the as-constructed heat pipe-assisted PCM based BTM is feasible and effective with a relatively longer operation time and more suitable temperature. The experimental results show that the temperature maldistribution of battery module can be influenced by heat pipes when they are activated under high discharge rates of the batteries. Moreover, with forced air convection, the highest temperature could be controlled below 50°C even under the highest discharge rate of 5C and a more stable and lower temperature fluctuation is obtained under cycling conditions. Meanwhile, the effectiveness of further increasing air velocity (i.e., more fan power consumption) is limited when the highest temperature continues to reduce at a lower rate due to the phase transition process of PCM. These results are expected to provide insights into the design and optimization of BTM systems.
•The performance of a photovoltaic-thermoelectric hybrid system is investigated.•An integrated phase change material/cobalt oxide nanofluid heat sink is proposed.•Around 14% higher electrical power ...is experimentally achieved by this heat sink.•The exergy efficiency of the unit is improved by 17.8% at noon.
Nowadays, photovoltaic panels have been known as effective devices to harness solar energy. These panels mainly convert the UV and visible areas of the solar spectrum into electricity and the rest of the energy is dissipated. One of the favorable methods to take advantage of such dissipated heat is to combine thermoelectric generators (TEG) utilizing the IR area of the solar radiation with photovoltaic panels. Having the different and opposite impact on the efficiency of thermal photovoltaic cells (PV/T) and thermoelectric generators (TEG), the system operating temperature appears as a critical parameter in the productivity of a PV/T-TEG hybrid unit. In the present study, a novel heat sink for a PV/T-TEG hybrid system is introduced. The effectiveness of simultaneous usage of the Co3O4/water nanofluid and the improved phase change material (paraffin wax/Alumina powder) as a cooling method on the performance of the PV/T-TEG is examined throughout an experimental study. Then, the overall electrical, thermal and exergy efficiency of such a system is compared to the units with divers working fluids including water and 0.25%, 0.5%, and 1% nanofluid and the unit consisting of 1% nanofluid with non-enhanced PCM cooling method. The results reveal that using 1% nanofluid with enhanced PCM, as a cooling method, would improve the overall electrical efficiency by 12.28% compared to water cooling technique. Also, an increase of 11.6% in the exergy efficiency of the PV/T-TEG is observed in comparison with PV/T-TEG with the water cooling method. Hence, it could be concluded that the combination of this unit could contribute to harnessing solar energy more efficiently, compared to solo photovoltaic panels.
•Optimisation of PCM based cooling coupled with liquid cooling system.•System weight and consumption of different configurations is evaluated.•Suggesting a 2-sided cold plates hybrid system for BTMS ...of pouch cells.•Suggested hybrid BTMS can withstand cell-to-cell variation of battery cells.
In this paper, a novel design for hybrid battery thermal management systems (BTMS) is proposed and evaluated from the economic and engineering perspectives. Numerical models are compared with phase change materials (PCM) BTMS. Further, the suggested hybrid cooling system’s thermal performance at the pack level is investigated considering cell-to-cell variation. A three-dimensional thermal model is used for the numerical simulation of the battery cooling system. The probability distributions is utilised for the cell-to-cell variations of a 168-cell battery pack. Results shows that for a 53 Ah lithium-ion battery (LIB) under a 5C discharge rate, a hybrid cooling system with two-sided cold plates can reduce the maximum temperature from ∼64 ∘C to 46.3 ∘C with acceptable system weight and power consumption, which is used for further pack level simulation. It is concluded that the two-sided cold plate hybrid design system can manage the maximum average temperature as well as temperature difference of cells in the desirable range at extreme cases.
•Effect of EHD with nanoparticles inclusion on the melting of Paraffin wax have been explored.•Melting of Nanocomposite under the influence of buoyancy, Coulomb and Dielectric force is ...investigated.•EHD effect on melt pool evolution is more predominant at lower thermal Rayleigh number.•A 50 % increase in the melting rate with EHD at an optimum nanoparticle concentration of 5 %.
The phase change materials (PCM) are having tendency to store thermal energy during its melting (charging) and release this during solidification (discharging) process. Among many materials, organic phase change materials are most suitable for different engineering applications due to their better thermal stability over repeated phase change cycles. However, their low thermal conductivity limits the energy storage capacity. Adding nanoparticles alone is not sufficient to improve its energy storage performance significantly due to weak convection current. Therefore, a numerical investigation is done here to study the energy storage performance improvement of PCM nanocomposites using an external electric field. The governing energy and momentum transport equations along with Poisson’s equation for electric potential and Nernst-plank equation for charge conservation are solved numerically using the finite volume method. A source based implicit enthalpy model is adopted for modeling the phase change of PCM. The effect of nanoparticle concentration, Electric Rayleigh number, charge injection number, thermal Rayleigh number and effect of dielectric force on melting characteristics of PCM nanocomposite were studied. It is found that there is significant improvement in melting rate of nanocomposite containing 5 % nanoparticles with 28 % increase in the liquid fraction. Moreover, Due to electric field, Coulomb force plays a great role in improving the heat transport when natural convection is weak and there is an enhancement of 50 % liquid fraction at Rayleigh number of 1 × 103. It is observed that even at zero gravity, the effect of electric field shows 90 % melting fraction of phase change materials in the cavity. The effect of charge injection has a significant role in enhancing the melting of PCM nanocomposite. There is also a comparative study of both Coulomb force and dielectric force. It is found that the dielectric force has no such effect on improving the melting of PCM nanocomposite.
•Inclusion of n-eicosane reduces temperature more significantly than paraffin wax.•A higher latent phase completion time was found in case of 3mm diameter pin-fin.•A higher enhancement in operation ...time is obtained in case of 3 mm diameter pin-fin.•The maximum thermal capacities of 2.24kJ/K and 2.90kJ/K are obtained for 3mm tpin-fin.•Thermal conductance of 6.95×10-1W/K and 5.69×10-1 are obtained for paraffin wax and n-eicosane.
The present paper covers the comparison of two different configurations (square and circular) pin-fin heat sinks embedded with two different phase change materials (PCMs) namely paraffin wax and n-eicosane having different thermo-physical properties were carried out for passive cooling of electronic devices. The pin-fins, acting as thermal conductivity enhancers (TCEs), of 2mm square and 3mm circular fin thickness of constant volume fraction of 9% are chosen and input heat fluxes from 1.2kW/m2 to 3.2kW/m2 with an increment of 0.4kW/m2 are provided. Two different critical set point temperatures (SPTs) 45°C and 65°C are chosen to explore the thermal performance in terms of enhancement ratios, enhancement in operation time, latent heating phase duration, thermal capacity and conductance. The results show that 3mm diameter of circular pin-fins has the best thermal performance in passive thermal management of electronic devices.
Integrating phase change material (PCM) into building envelopes significantly reduces building energy consumption and improves indoor environment. Among different integration techniques, ...macro-encapsulation allows for an efficient, safe and convenient way of using PCM, and its applications have been widely investigated in recent years. However, this study argues that there is a lack of a systematic analysis regarding the thermal performance of macro-encapsulated PCM, particularly for building envelope applications. Also, a number of important issues have seldom been addressed such as material selection and PCM melting processes at a component level, and optimal locations at a system level. Such a research gap remains a barrier to architects and engineers succeeding at making rational decisions during building design stages, thereby achieving the optimal building performance. This paper aims to provide a comprehensive overview of macro-encapsulated PCM and its integration into building envelopes. The discussion mainly includes: definition and material selection for PCM macro-encapsulation, common macro-encapsulation forms and PCM melting processes within these forms, the optimal locations of systems in building envelopes, and thermal performance enhancement for PCM and shells. In addition, the key issues in future studies are discussed. It is hoped that this comprehensive review will contribute to a deeper understanding of the design and application of macro-encapsulated PCM in building envelopes.
•Comprehensive review on macro-encapsulated PCM in building envelopes.•Definition and material selection for PCM macro-encapsulation.•Common macro-encapsulation forms and PCM melting processes within these forms.•Thermal performance enhancement for macro-encapsulated PCM.
•Two nano-enhanced fatty acids with Tm within building application were developed.•Capric acid and capric–myristic mixture were successfully enhanced by adding nSiO2.•The NEPCM obtained showed high ...thermal conductivity and specific heat capacity.•Both are thermal-stable, ensure long-term performance and behave as Newtonian fluid.•NEPCM are promising available materials to store thermal energy.
Fatty acids are promising organic phase change materials (PCMs) for thermal energy storage (TES) in buildings because of their high storage capacity, non-toxic nature and little subcooling. Their phase change temperatures make them suitable for heating, ventilating and air conditioning (HVAC) applications in the building sector. However, one of their main drawbacks is their poor thermal conductivity which limits their application. In the present study two fatty acids within the building application temperature range, capric acid (CA) and capric–myristic acid (CA–MA) eutectic mixture, were nano-enhanced throughout silicon dioxide nanoparticles (nSiO2) addition (0.5 wt.%, 1.0 wt.% and 1.5 wt.%). Main properties of the nano-enhanced phase change materials (NEPCM) obtained were characterized by means of differential scanning calorimetry (DSC), Hot wire technique, Fourier transformed infrared (FT-IR) spectroscopy, thermogravimetric analyses (TGA), scanning electron microscopy (SEM), and rheological measurements. Furthermore, their long-term performance was evaluated after 2000 cycles by means of cycling stability tests. The NEPCM obtained showed high thermal conductivity and specific heat capacity. Additionally, both are thermally stable within their working temperature range and ensure a long-term performance.
The objective of this study is to overcome the leakage and low thermal conductivity problems of paraffin as PCMs (phase change materials) for thermal energy storage by impregnating SEBS/paraffin/HDPE ...FSPCMs (form-stable phase change materials) into metal foam. The form-stable composites were prepared by absorbing paraffin into the network of powder-like styrene-b-(ethylene-co-butylene)-b-styrene (SEBS) triblock copolymer and covering high-density polyethylene (HDPE) on pre-prepared SEBS/paraffin mixture. The composites were characterized by using differential scanning calorimetry (DSC), Scanning electron microscope (SEM), Fourier Transform Infrared Spectrometer (FT-IR), X-Ray Diffraction (XRD) and Hot disk. Paraffin leakage was investigated by accelerated degradation test at 80°C. The melting temperature and latent heat of the composites were determined as 50.56°C and 151.6J/g, respectively. FT-IR results revealed good chemical compatibility among paraffin, SEBS and HDPE. SEM images and XRD test results demonstrated that the paraffin had uniformly dispersed into SEBS. This composite was testified able to keep paraffin from seepage with only 2.39wt% of paraffin loss after 50 thermal cycles test (150h). In addition, the thermal conductivity of SEBS/paraffin/HDPE was 0.272W/mK, which was increased up to 2.142W/mK when copper foam was embedded in the composite.
•SEBS/paraffin/HDPE form stable PCM was prepared using a direct impregnation method.•Microstructure and thermal properties of the composites were examined.•The FSPCMs show nearly no leakage under accelerated degradation thermal tests.•The FSPCMs are able to impregnate into metal foam to enhance heat transfer.
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