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The study describes experimental data on thermal tests during the condensation of HFE7100 refrigerant in a compact heat exchanger. The heat exchanger was manufactured using the additive 3D printing in metal. The material is AISI 316L steel. MPCM slurry was used as the heat exchanger coolant, and water was used as the reference medium. The refrigerant was condensed on a bundle of circular tubes made of steel with an internal/external diameter of di/de = 2/3 mm, while a mixture of water and phase change materials as the coolant flowed through the channels. Few studies consider the heat exchange in condensation using phase change materials; furthermore, there is also a lack of description of heat exchange in small-sized exchangers printed from metal. Most papers deal with computer research, including flow simulations of heat exchange. The study describes the process of heat exchange enhancement using the phase transition of coolant. Experimental data for the mPCM slurry coolant flow was compared to the data of pure water flow as a reference liquid. The tests were carried out under the following thermal and flow conditions: G = 10–450 [kg m−² s−1], q = 2000–25,000 [W m−²], and ts = 30–40 [°C]. The conducted research provided many quantities describing the heat exchange in compact heat exchangers, including heat exchanger heat power, heat exchange coefficient, and heat exchange coefficients for working media. Based on these factors, the thermal performance of the heat exchanger was described. External characteristics include the value of the thermal power and the heat exchange coefficient as a function of the mass flow density of the working medium and the average logarithmic temperature difference. The performance of the heat exchanger was presented as the dependencies of the heat exchange coefficients on the mass flux density and the heat flux density on the heat exchange surface. The thickness of the refrigerant's condensate film was also determined. Furthermore, a model was proposed to determine the heat exchange coefficient value for the condensing HFE7100 refrigerant on the outer surface of a bundle of smooth tubes inside a compact heat exchanger. According to experimental data, the calculation results were in good agreement with each other, with a range of 25%. These data can be used to design mini condensers that are widely used in practice. [ABSTRACT FROM AUTHOR]

Highlights: Research progress of advanced optical fiber sensors in traction batteries and energy storage batteries is summarized. The embedded application mechanisms of different optical fiber sensors in batteries are discussed. Advanced optical fiber sensors adapting to batteries with diverse materials are reviewed. Advanced optical fiber sensors driving the development of future smart batteries are prospected. The battery technology progress has been a contradictory process in which performance improvement and hidden risks coexist. Now the battery is still a "black box", thus requiring a deep understanding of its internal state. The battery should "sense its internal physical/chemical conditions", which puts strict requirements on embedded sensing parts. This paper summarizes the application of advanced optical fiber sensors in lithium-ion batteries and energy storage technologies that may be mass deployed, focuses on the insights of advanced optical fiber sensors into the processes of one-dimensional nano–micro-level battery material structural phase transition, electrolyte degradation, electrode–electrolyte interface dynamics to three-dimensional macro-safety evolution. The paper contributes to understanding how to use optical fiber sensors to achieve "real" and "embedded" monitoring. Through the inherent advantages of the advanced optical fiber sensor, it helps clarify the battery internal state and reaction mechanism, aiding in the establishment of more detailed models. These advancements can promote the development of smart batteries, with significant importance lying in essentially promoting the improvement of system consistency. Furthermore, with the help of smart batteries in the future, the importance of consistency can be weakened or even eliminated. The application of advanced optical fiber sensors helps comprehensively improve the battery quality, reliability, and life. [ABSTRACT FROM AUTHOR]

Wearable thermoelectric generators have great potential to provide power for smart electronic wearable devices and miniature sensors by harnessing the temperature difference between the human body and the environment. However, the Thomson effect, the Joule effect, and heat conduction can cause a decrease in the temperature difference across the thermoelectric generator during operation. In this paper, phase change materials (PCMs) were employed as the heat sink for the thermoelectric generator, and the COMSOL software 6.1 was utilized to simulate and optimize the power generation processes within the heat sink. The results indicated that with a PCM height of 40 mm, phase transition temperature of 293 K, latent heat of 200 kJ/kg, phase transition temperature interval of 5 K, thermal conductivity of 50 W/(m·K), isobaric heat capacity of 2000 J/(Kg·K), density of 1000 kg/m3, and convective heat transfer coefficient of 10 W/(m·K), the device can maintain a temperature difference of 18–10 K for 1930 s when the thermoelectric leg height is 1.6 mm, and 3760 s when the thermoelectric leg height is 2.7 mm. These results demonstrate the correlation between the device's output performance and the dimensions and performance parameters of the PCM heat sink, thereby validating the feasibility of employing the PCM heat sink and the necessity for systematic investigations. [ABSTRACT FROM AUTHOR]

Phase change microcapsules are a type of energy storage material that can affect temperature changes by changing its material state and releasing or absorbing latent heat. In this paper, the temperature effect of phase change microcapsules on permeable concrete is investigated. Cooling, heating, and snow melting tests were performed on ordinary permeable concrete and test blocks with different contents of phase change microcapsules. The results indicate that the addition of phase change microcapsules to ordinary permeable concrete has several benefits. First, it effectively raises the internal temperature of concrete in cold conditions. Second, it prolongs the heating duration of concrete in high-temperature environments. Last, it helps in reducing the maximum temperature reached by the concrete. Moreover, the heat storage capacity of phase change microcapsules prevents the refreezing of melted snow water within the concrete. With the increase of the content of phase change microcapsules, the temperature-regulating effect of the test blocks is improved. To sum up, phase change materials can exhibit temperature-regulating effect on permeable concrete under different environmental conditions and have wide applications in the design, manufacture, and performance research of permeable concrete. [ABSTRACT FROM AUTHOR]

Efficient thermal energy distribution and rational energy management are effective solutions to address the significant and fast-ascending energy consumption in building heating, ventilation, and air conditioning (HVAC). Phase change material (PCM) slurries with excellent thermal energy transportation and storage characteristics have been recognised as promising secondary refrigerants to simultaneously facilitate efficient heat/cold transport and effective thermal energy storage in air conditioning systems. Among various PCM slurries, salt hydrate PCM slurries have attracted increasing attention in recent years due to their many inherent advantages. This paper presented the preparation, characterisation, and property modification of a CaCl 2 ·6H 2 O slurry based on a methodology proposed for optimal salt hydrate PCM slurry development. Theoretical modelling was first carried out to assess the availability of salt hydrate PCM slurries based on the phase diagram and solid fraction, followed by a series of property measurements to reveal the mechanisms and address the problems behind the phase transition, crystal particle morphology, stability and rheologic characteristics, using nucleating agents, surfactants and stabilisers. It was found that the salt hydrate PCM slurry developed provides a unit volume enthalpy twice that of water over the phase change temperature range of 5°C, together with acceptable fluidity. The results also showed that the PCM particle size can be well controlled, and the slurry can be stabilised, with the assistance of surfactants and stabilisers. Compared to other types of PCM slurries, the proposed salt hydrate PCM slurry has the advantages of being cost-effectiveness, easy preparation, adjustable phase change temperature, etc. , which is promising to facilitate energy saving and rationalisation in building HVAC. [ABSTRACT FROM AUTHOR]

Phase change materials (PCMs) are the materials that can absorb and release energy during their phase transition. The materials have become ubiquitous but still face challenges. The inevitable transition from solid phase to liquid phase in these materials during operation limits their utility in application areas that require leak-proof properties like orthopaedic mattresses or gel packs, or applications requiring self-load-bearing capabilities (such as ceiling tiles and building walls). Entrapment of PCM in porous matrices is one of the promising methods of capturing the PCM and limiting the flow of materials in the liquid phase. The present study discusses the preparation of exfoliated graphite from commercially available intercalated graphite. The process of exfoliating the intercalated graphite has been holistically characterized using x-ray diffraction, Fourier transform infrared spectroscopy (FTIR), and scanning electron microscope (SEM). The graphite with a surface area of 47.37 cc/g with a purity of 99% was found to have a maximum absorption of 80% (w/w) stearic acid as PCM. In addition, this paper investigates two synthetic routes to prepare the shape-stabilized PCM. The blends are characterized and compared along six indicators: transition point, latent heat capacity, thermal conductivity, exudation behavior, FTIR, and SEM. Composite 1 refers to stearic acid absorbed in the exfoliated graphite. Composite 2 refers to the stearic acid absorbed in exfoliated graphite which is further treated with an elastomer SEBS. The leak test performed on both blends signifies that SEBS is an essential ingredient. The PCM composition optimized in this study can unlock various thermal applications with critical requirements where direct exposure of chemicals to the user is unacceptable. Further, the study itself is envisaged to serve as a framework to develop enhanced shape-stabilized PCMs with tuneable thermal conductivity and extended operation life in application areas where leakage in liquid phase is a concern. [ABSTRACT FROM AUTHOR]

PCMs are an ideal energy storage material, widely used in construction and have gradually become a hot spot for research. To address the shortcomings and deficiencies of single PCM, this paper combined myristic acid (MA), palmitic acid (PA) and paraffin slice (48#, PS) to prepare a ternary system of PCM by using a melt blending method. The study found that the lowest eutectic point is reached when MA : PA : PS=43.4 : 18.6 : 38, with phase change temperature and enthalpy of phase change of 39.28 °C and 135.83 J/g, respectively, showing better superiority. Moreover, FT‐IR and XRD also indicated that no new functional groups appeared in this ternary PCM, no new substances were produced, and all were simple physical bonding. TG showed that MA‐PA‐PS does not decompose below 127.95 °C and has good thermal stability. Finally, it was indicated that its thermal reliability is good after 500 thermal cycles of MA‐PA‐PS. Therefore, as a new type of energy‐saving material, this ternary PCM has good reliability and superiority, and has good application prospects. [ABSTRACT FROM AUTHOR]

• Experiments were conducted on an insulated box containing either one or two PCMs. • Experimentally derived thermal resistances were used in a zeroth order thermal model. • The model predicts the duration of the product kept within a temperature range. • The model was validated with 9 configurations and three ambient temperatures. • The use of two PCMs reduced freezing while retaining high thermal energy storage. Portable transport passive-type refrigeration systems keep products in specific temperature ranges for several days without electricity. Phase change material (PCM) is often combined with insulation panels to form an insulated box. This paper presents the effect of utilizing multiple PCMs with different melting temperatures and heat capacities on product storage and product temperature abuse. Two PCMs with different transition temperatures were thermally coupled, forming a cascade passive refrigeration system. The primary PCM (water) had the largest storage capacity. At the same time, the secondary PCM acted as a thermal buffer to prevent the temperature abuse, namely freezing, of the product carried inside the box. Modifications were made to an existing state-of-the-art refrigerated transport box to install PCM-based passive refrigeration systems that extended the refrigeration performance while maintaining the same envelope and interior volume. Experiments were conducted at ambient temperatures of 20 °C, 35 °C, and 42 °C while the temperature inside the container remained below 6 ℃ for several days. Effective thermal resistance values for the insulated refrigerated transport box and between the PCMs and the product inside the box were determined experimentally. A semiempirical numerical thermal model was developed to predict the duration, and the average error between the predicted duration and the data was 9.7 %. Correlations from the literature were also compared to estimate the transport box performance for various configurations, and the results indicated that such correlations estimated the storage duration satisfactorily only for simple configurations of the insulated box. [Display omitted] [ABSTRACT FROM AUTHOR]

Photovoltaic panels may capture up to 80% of the sun' radiant energy; however, depending on the panel composition, only a small portion is converted to electricity. The remaining energy causes the surface temperature of the panel to increase. Temperature rise at the panel's surface is a critical problem affecting efficiency and shortening panel lifespan; hence, thermal management of the photovoltaic module during operation is vital. Hybrid designs that cogenerate electricity and heating (hot water or space heating) have been proven to be a feasible solution. A photovoltaic panel coupled with heat pipes and phase change materials could be a promising solution to generate electricity and utilize the waste heat simultaneously. This paper presents a mathematical approach to examine the dynamic performance of the photovoltaic thermal panel integrated with phase change material and heat pipe (HP-PV/T-PCM) setup. Furthermore, a comparison study is conducted to compare the simulation and experimental test results to validate the proposed model's accuracy. The effects of melting point temperature of phase change material, water flow rate, and the heat pipes number on the main output parameters of the proposed setup are investigated. The results show that adding the PCM layer to the system increases the heat gain by 7.58%. At the design condition, daily average electrical and thermal power outputs could reach 58.56 and 277.167 W/m2 for the HP-PV/T-PCM system and 57.53 and 257.642 W/m2 for the HP-PV/T system, respectively. In addition, the daily average thermal, electrical, and overall efficiencies are obtained at 46.33%, 9.79%, and 53.65% for the HP-PV/T-PCM system and 43.06%, 9.62%, and 50.18% for the HP-PV/T system, respectively. Hence, compared with the PVT/HP setup, the electrical, thermal, and overall efficiencies of the PVT/HP/PCM system have increased by 1.77%, 7.59%, and 6.92%, respectively. [ABSTRACT FROM AUTHOR]

The research on latent heat storage technology is beneficial for the large-scale popularization and application of energy storage technology. In order to solve the difficulties in the latent thermal energy storage (LTES) technology, numerical studies of the solid–liquid phase-change process of LTES units using the enthalpy-porosity method have become research hotspots. Among them, the importance of studying the mushy-zone parameter has been neglected. In this paper, a two-dimensional numerical model is created based on the enthalpy-porosity method to investigate the effects of different mushy-zone parameters within a wide range [104–108 kg/(m3·s)] on the melting and solidification processes of the spherical phase change material capsule. A comprehensive examination of the fluid flow and heat transfer characteristics during two phase-change processes is conducted. Meanwhile, the morphology of the solid–liquid phase boundary and the evolution of the mushy zone under different mushy-zone parameters are discussed in detail. It is worth mentioning that a new analytical perspective is innovated by proposing the "eccentricity phenomenon," and the eccentricity law is further explored. The results show that the influence mechanisms of the mushy-zone parameters on the melting and solidification processes differ greatly. This paper emphasizes the significance of exploring the mushy zone and provides adequate guidance for future simulation studies to determine the mushy-zone parameter. [ABSTRACT FROM AUTHOR]

Tetrabutylammonium bromide (TBAB) is considered a promising alternative cold energy storage material. Due to the high dissociation heat of phase transition at an atmospheric pressure of 278–293 K, which reaches 200–500 kJ/kg, this substance is considered an effective cold energy storage medium for air conditioning systems. In this paper, the cold storage crystallization process of TBAB solution with different concentrations was tested by conducting experiments and the phase transition's temperature and latent heat were measured. Finally, the growth characteristics of TBAB hydrate crystals with different concentrations (10%, 20%, 30% and 40%) were analyzed. Considering the cold storage temperature, phase transformation temperature and latent heat, the cold storage effect is the best when 40% TBAB solution is used. Although single substance phase change materials have a long service life, they have problems with low thermal conductivity and high undercooling. Therefore, researchers usually improve the performance of phase change materials by adding other auxiliary materials, thereby enhancing their application prospects. Among these auxiliary materials, adding nano additives to phase change materials can significantly improve latent heat, thermal conductivity and nucleation ability, while also reducing undercooling. Therefore, we studied the influence of different nano-additives (Al2O3, SiC, TiO2 and ZnO) on phase change materials. The composites with excellent properties were screened by cooling step cooling curve and differential scanning calorimeter (DSC). Compared with pure TBAB solution, the phase transition latent heat of the composite phase change materials (PCMs) prepared by adding nanoparticles were significantly increased. The results show that adding nano-SiC into 40% TBAB solution can obtain better performance. This work not only provides reference for the further research, but also a sight to design the phase change materials for the application of new phase change cold storage materials. [ABSTRACT FROM AUTHOR]

In order to solve the problem of the performance of mixed alkane phase change energy storage materials, this paper proposes the modelling research of mixed thermodynamic model based on new materials. In this paper, the thermodynamic performance of binary mixed alkane system is studied, the influence of phase transition temperature, phase transition enthalpy and its composition on the mixed alkane system is explored, and its solid-liquid phase diagram is drawn. We used different thermodynamic models to predict the phase transition temperature and enthalpy in the melting process of binary mixed alkanes, which were mutually verified with the experimental results. The experimental results show that C9-C10 and C9-C11 systems exhibit eutectic behavior. The eutectic components are 88% (mass fraction, the rest is the same) C9-12% C10 and 90% C9-10% C11. The eutectic temperatures are 218.25 K and 215.15 K, respectively. The C8-C9 system has peritectic phenomenon, C10-C11 system shows complete mutual solubility, and their minimum melting points are 200.25 K and 234.35 K, respectively. Conclusion is that the C9-C10 and C9-C11 eutectic systems are suitable for low temperature phase change materials in the temperature range of 210-220 K, providing data reference for their application in low temperature energy storage. [ABSTRACT FROM AUTHOR]

Transition temperature is significant in determining applications of phase change materials. In this paper, PEG2000 and PEG4000 were used as soft segments and MDI and 3,3ʹ-Dichloro-4,4ʹ-diaminodiphenylmethane (MOCA) were used as hard segments. Several polyurethane solid–solid phase change materials (PUSSPCMs) were synthesized by adjusting the mass ratio of PEG4000 and PEG2000. Based on the differential scanning calorimeter test, this paper studied the relationship between the mass ratio of PEG2000 and the phase transition temperature. The influence mechanism of phase change temperature was revealed from molecular structure, crystallization properties, and surface morphology. Furthermore, PUSSPCMs were tested for leakage and the thermal stability. The results showed that the synthesized PUSSPCMs had no liquid leakage during the heating process. There was a good linear relationship between the mass ratio of PEG2000 and phase transition temperature. The thermal decomposition onset temperature was above 230 °C. [ABSTRACT FROM AUTHOR]

A cold storage unit can store the cold energy off-peak and release it for building cooling on-peak, which can reduce the electricity load of air conditioning systems. n-tetradecane is a suitable cold storage material for air conditioning, with a phase change temperature of is 4–8 °C and a phase change enthalpy of 200 kJ/kg. However, its low thermal conductivity limits the application of n-tetradecane for high-power cold storage/release. This paper prepares a tetradecane/expanded graphite (EG) composite phase change material (CPCM), whose thermal conductivity can be increased up to 21.0 W/m·K, nearly 100 times over the raw n-tetradecane. A novel model to predict the maximum loading fraction of paraffin in the EG matrix is presented, with an error within 1.7%. We also develop a thermal conductivity model to predict the thermal conductivity of the CPCM precisely, with an error of less than 10%. In addition, an innovative spiral wave plate cold storage tank has been designed for the tetradecane/EG composite. The power and energy density of the cold storage tank are significantly improved compared to that of raw tetradecane. The energy density reaches 40 kWh/m3, which is high among the organic PCM thermal storage tank. This paper shows the significance of thermal conductivity enhancement in designing a cold storage tank. [ABSTRACT FROM AUTHOR]

The integrated phase change materials (PCM) solar wall can store solar energy effectively, which has a broad application prospect. However, the integrated PCM solar wall cannot completely release heat at night. In this paper, the evaporator of the heat pump system is embedded in the integrated PCM solar wall, which can realize the combination of active and passive utilization of solar energy. A numerical study on the thermal storage/release characteristics of the integrated PCM solar wall with an embedded evaporator was carried out in this paper considering its two-dimensional heat transfer. The effect of the thermal release mode, the thermophysical parameters of PCM and the solar radiation intensity on the thermal storage/release characteristics was studied. The simulation results showed that the active thermal release mode increased the released heat by 33.33 kJ/kg, and the proportion of the released heat to the stored heat increases by 30.12%, compared with the passive thermal release mode. Moreover, the increase of the phase transition temperature and the thermal conductivity of PCM can increase the stored heat and released heat, and the latent heat of PCM will increase the stored heat and decrease the released heat. The conclusion can provide a theoretical basis for the research of active and passive solar systems. [ABSTRACT FROM AUTHOR]

• Thermo-physical characterization of micro-encapsulated PCM suspensions. • Phase transition in micro-particles detected by calorimetry and densimetry. • Shell induces metastable rotator observed during solidification. • Models assessment accounting for the properties of PCM suspensions. [Display omitted] Despite the growing popularity of phase change materials (PCM) and suspensions of micro-encapsulated phase change materials (mPCM) in both industrial and scientific applications, their properties characterization remains partial and mainly limited to thermal properties. The characterization of such suspension is a crucial aspect for comprehending their behavior and optimizing their performance. This paper is dedicated to a wide characterization of two suspensions containing micro-encapsulated phase change material. In pursuit of a thorough understanding, we also extend our characterization efforts to the bulk PCM encapsulated within the particles. Our primary focus is on determining the materials thermal properties such as latent heat and specific heat capacity using differential scanning calorimetry. Different cooling and heating rates have been employed in our measurements. Regarding our experiments, the bulk phase change material is predominantly identified as octadecane. Results obtained from calorimetry are then compared between the bulk PCM and the mPCM suspensions. By comparing the magnitudes of latent heat obtained for suspensions with the bulk material, we can accurately determine the mass fraction of PCM within each suspension. Noteworthy, during the solidification process an additional latent heat peak is observed only for the encapsulated PCM. The density of the materials is also measured. The phase change of PCM included in the capsules can be observed in densimetry: within the studied temperature range (283.15–306.15 K), the most significant density variations occur during intervals associated with phase change transitions. In ranges where the PCM, included in the capsules, is in a single-phase state (solid/liquid), we provide linear laws that account for density variations with temperature. Finally, our characterization work focuses on the rheological properties of the materials. While the bulk PCM in liquid phase exhibits a Newtonian viscosity, mPCM suspensions present a non-Newtonian viscosity. Both shear-thinning and shear-thickening behaviors are observed depending on the suspension particle volume fraction ϕ of mPCM. This paper concludes with a full comparison of our characterization results with models and correlations proposed in the literature. [ABSTRACT FROM AUTHOR]

• Almost all the investigated PCMs are compatible with aluminium, copper, stainless steel, and plastic. • Differences in thermal behaviour were observed despite the same operating conditions were applied. • The thermophysical and transport properties deeply affect the thermal performance of PCMs. • The charging time differs from the discharging one despite the same operating conditions. • The presence of metal lattice structures reduces the charging time more than the discharging one. Refrigeration, air conditioning and heat pump sector represents between 25 and 30% of the global consumption of electricity and this figure is expected to rapidly grow due to the current trend of electrification. To increase the efficiency of these systems or to maximize the use of renewable energy, latent thermal storage systems are being studied and recommended. However, there is a lack of reliable design rules based on trustable data that could help the thermal experts to design efficient and cost-effective latent thermal energy storage. This paper follows a previous work recently published (Longo et al., 2022) where the thermo-physical and transport properties of a few low temperature PCMs (i.e. 2–9 °C of melting temperature) were measured and discussed. In the present work, the attention is focused on two other fundamental aspects: the PCMs' compatibility with the most common construction materials and their thermal behaviour during the solid/liquid phase change. The collected results will contribute to add currently unavailable data in the literature and to highlight interesting insights on the performance of the selected PCMs. [Display omitted] [ABSTRACT FROM AUTHOR]

Terahertz (THz) metasurfaces have emerged as powerful tools to modulate the wavefronts of THz radiation fully. Smart designs and fabrication are essential for enhancing the flexibility and encryption security of THz metasurfaces. In addition to digital coding metasurfaces and microelectromechanical systems, one method to realize dynamic THz metasurfaces is to utilize an active material. In this paper, a dynamic THz metasurface, which is combined with the phase‐change material VO2 and can be thermally controlled to achieve optical encryption, is proposed. Based on the electromagnetically induced transparency effect and by arranging the antennas in advance according to a specific hologram, a secret image can be encoded into the metasurface. At room temperature, the transmitted light field is an irregular light spot with no useful information. If the temperature increases above the phase‐change temperature, the encrypted hologram can be reconstructed. Moreover, owing to the distinct characteristics of VO2, the phase‐change temperature required during decryption is not very high, and the entire process is reversible. It is expected that, in combination with updated processing technology, such metasurfaces can be practically applied to the next generation of optical encryption or optical anticounterfeiting in the future. [ABSTRACT FROM AUTHOR]

Photonic crystal fibers (PCFs) have recently attracted compelling attention because of their numerous applications, particularly in the mid-infrared (mid-IR) wavelength region. In this paper, we have presented and analyzed mid-IR optical modulator based on phase-changing material (PCM) known as germanium-antimony-tellurium (GST) and D-shaped PCF. The modulation process can be performed as the GST material's phase undergoes a transition between amorphous (on) and crystalline (off) states. To analyze the proposed design numerically, full vectorial finite element method (FVFEM) is employed. Further, we studied the light propagation through the suggested structure using 3D finite difference time domain (FDTD) method. The optical losses of the fundamental transverse electric (TE) mode supported by the reported structure in the two GST states are studied. The obtained extinction ratio (ER) of the proposed modulator approaches 302.61 dB, whereas the insertion loss (IL) is less than 0.00014 dB throughout the wavelength range from 3 to 5.8 μm at a device length (LD) of 0.2 mm. Therefore, the suggested modulator can be utilized in photonic integrated circuits that require high ER, very low IL, and large optical bandwidth. [ABSTRACT FROM AUTHOR]

Common phase change materials (PCMs) have serious shortages, and the most important one is the low thermal conductivity. This issue makes the phase change process a time-consuming period that decreases the performance of thermal storage units. This paper concentrated on improving energy and exergy performance with the aid of an air–PCM heat exchanger, which could be employed for free cooling of buildings. For the heat exchanger, the PCM of Rubitherm 22 °C high capacity (RT22HC) and the nanoparticles of multi-wall carbon nanotube were employed. The initial charging and discharging experiments showed that due to thermal conductivity enhancement, melting and solidification periods decreased using nano-PCM with three concentrations of 0.1, 0.2, and 0.5 mass% compared to the PCM without nanoparticles. Moreover, the highest exergy and energy efficiencies were obtained for the case of nano-PCM 0.5 mass% during the charging process and the values were 11.03 and 21.33%, respectively. Experiments with nano-PCM 0.5 mass% were accomplished during three continuous days. The results demonstrated that the heat obtained from nano-PCM 0.5 mass% encapsulations varied with weather conditions. In addition, the output energy and exergy rose with sunrise and fell with sunset. Finally, an economic analysis was carried out for cold climate conditions. The results indicated that the whole invested capital expenditures will return in the ninth year of exploitation. [ABSTRACT FROM AUTHOR]

This paper presents the development of a methodology for using simulation to test decentralised façade ventilation systems with PCM exchangers and its validation with experimental data. Two approaches were compared to simulate the operation of an exchanger filled with phase-change material. In Method A, the geometry consisted of an air domain and a phase-change material domain, located in the cylinders of the exchanger. In this method, the phase transition was not modelled, but the specific heat was made temperature-dependent, wherein within the limits of the melting point, the specific heat is increased to a level that mimics the amount of latent heat from melting and solidification of the phase-change material. In Method B, the geometry consisted only of the air domain, and the temperature was set on the cylinder wall surfaces at each time step using UDFs. When comparing the methods, the temperature difference at the individual measuring points was no greater than 1 K and the resulting exchanger efficiencies did not differ by more than 5%. It was noted that when the phase-change material was modelled in the software with Method A, the results provided better representation of the values obtained in the experiment. Validation of the models was carried out by comparing the experimental results from the real tests with the simulation results of methods A and B. It demonstrated that both models correctly reflected the operation of the exchanger, and that the efficiency results achieved did not differ by more than 6% compared to the experiment. A comparison of supply temperatures and exchanger efficiencies with numerical simulations using two methods is presented. Visual comparison of the temperature distribution in the flowing air and the temperature distribution on the cylinder walls is also presented. This article adds to existing scientific knowledge of computer simulation of exchangers used in façade ventilation units with phase-change material. [ABSTRACT FROM AUTHOR]

Solar energy coupling with energy storage is a popular technology in the energy field. How to achieve the high-efficiency application of solar energy is very important. Energy storage technology is the key issue in this aspect. Latent heat storage is a more efficient energy storage. In this paper, a visualization experimental platform of a latent heat storage system has been designed, and some performance data have been obtained. Hot water has been used as the heat transfer fluid, and paraffin wax has been used as the phase change material. The inclination angle of the tank is varied from the horizontal direction (0°) to the vertical direction (90°) by a step of 30°. The melting performance has been studied for three cases with inlet water temperature of 356 K, 361 K, and 366 K. The result shows that the inclination angle of the tank has a great influence on the melting process of the phase change material, and the temperature distribution of the material is obviously different. The result also shows that the testing point temperature (for testing point 1) varied from 341.31 K to 342.18 K when the inclination angle was 30° and 90°, respectively. However, the temperature of testing point 4 varied from 321.76 K to 335.03 K when the inclination angle was 30° and 90°, respectively. The results of this paper can provide a reference for the future pipe design and storage efficiency of latent heat storage systems. [ABSTRACT FROM AUTHOR]

In this paper, a new type of microencapsulated phase change materials (MPCMs) with docosane as the core and titanium dioxide (TiO2) as the shell was prepared by in situ polymerization. Its phase transition temperature was approximately 40 °C, and it can be used as a phase change material (PCM) in a low-temperature solar heat collection system. The properties of the new material were examined including the microstructure, the chemical elements on the surface of the microcapsules, and thermal conductivity. In addition, to obtain the optimized formula of the microcapsules, single-factor analysis on the emulsifier type, its mass fraction, ultrasonic oscillation time, pH, and core–shell ratio were performed. The results showed that the MPCMs prepared in this paper had a particle size of 2–5 μm and were spherical. Its surface was uniform and smooth without cracks, and the TiO2 was well dispersed around the docosane, completely coating the docosane without impurities. The MPCMs had good performance in terms of thermal properties and heat storage when using 0.40% SDS as an emulsifier, 10 min ultrasonic, a 3.5 pH value, and a 1:1 core–shell ratio. However, the stirring method, time, and experimental reaction temperature also affected the properties of the material, which was not studied in this experiment. We will continue to study these factors in the future. [ABSTRACT FROM AUTHOR]

Latent heat thermal energy storage is a promising technology because it can store more energy than conventional heat energy storage systems. Today, most of the waste heat is released into the atmosphere from different sources. The main emphasis of this study is to recover the waste heat produced by the condenser in the refrigeration system. The charging process of a phase change material (PCM) in spiral heat exchanger is studied for thermal storage purposes. In this experiment, waste heat is collected using Mystril alcohol (CH3(CH2)12CH2OH) phase-change material (PCM). A phase transition material is a substance with a high latent heat of transformation that changes into a new phase at a particular temperature. However, this paper shows how coil type tube can be employed as a tubulator to enhance its thermal characteristics including Nusselt (Nu) number and thermal performance. At different temperatures and mass flow rate, the amount of heat absorbed by PCM and that heat transferred to the cold water is analysed. [ABSTRACT FROM AUTHOR]

Summary: In this paper, the solidification process of the phase change material (PCM) in the shell‐and‐tube latent‐heat thermal energy storage unit (LTESU) strengthened by fin is studied. For improving the strengthening effect of fins on the solidification performance of shell‐and‐tube LTESU, this paper proposes a novel connected‐Y‐shaped fin. The novel fin is inspired by the interconnection of the internal texture of the lotus leaf, and the branches of the two‐level Y‐shaped fins are connected into a whole by three metal annuluses. The numerical simulation method is applied to investigate the influence of the connected‐Y‐shaped fin on the solidification performance of PCM. The effects of annulus position and fin width on solidification performance are studied and analyzed. At the same time, the effects of the connected‐Y‐shaped fin on the solidification process under different wall temperatures and the radius ratio of outer to inner tube (γi) are investigated. The results indicated that the connected‐Y‐shaped fin can significantly enhance the discharging performance of LTESU. Compared with the traditional two‐level Y‐shaped fins, the optimized connected‐Y‐shaped fin can shorten the PCM solidification time by 53.9%. The optimum width ratio of the connected‐Y‐shaped fin should be 2. The optimum radius ratio of the outer annulus, middle annulus, and inner annulus to the outer tube should be 0.91, 0.64, and 0.41, respectively. The scope of application of the conclusion is that Ste = 0.139 − 0.496, and γi = 0.083 − 0.167. Highlight: A novel connected‐Y‐shaped fin is proposed for the latent heat storage unit.The influences of fin structure parameters on the solidification process are discussed.Optimum fin parameters are recommended for maximizing the solidification rate.The novel fin can decrease the solidification time of PCM by 53.9%. [ABSTRACT FROM AUTHOR]

Summary: Microencapsulated phase change materials (MEPCMs) have made tremendous advancements in recent years, owing to their increased demand for a variety of energy storage applications. In this paper, current microencapsulation techniques, enhancement, and use of medium‐ and high‐melting phase change materials (PCMs) are reviewed, as well as their potential benefits and limitations. The most frequently employed PCMs for medium‐ and high‐temperature applications were recognized as salt‐based, metallic, inorganic compound, and eutectic. Meanwhile, polymethyl methacrylate (PMMA), polystyrene‐butylacrylate (PSBA), polyethyl‐2‐cyanoacrylate (PECA), and polyurethane were widely used as polymer shell materials for encapsulating medium‐ and high‐melting point PCMs via chemical method, whereas inorganic silica shell was synthesized via various techniques. Hydrolysis followed by heat‐oxidation treatment has been extensively studied since 2015 to encapsulate either metal or alloy within Al2O3 shells. Different techniques were developed to generate void between core and shell material to accommodate volume expansion during phase transition. Numerous approaches, including the incorporation of metal particles, carbon, and ceramic, have been found as ways to enhance the thermal performance of PCMs. Multiple storage arrangements were also established to be an effective way of enhancing the overall efficiency of medium‐high melting PCM storage systems. Finally, the paper highlights the potential of medium‐ and high‐melting temperature PCMs for solar power generation, solar cooking, and industrial waste heat recovering applications. [ABSTRACT FROM AUTHOR]

In this paper, heat transfer characteristics of phase change material in rectangular containers are numerically analyzed. The inclination angles of the container refer to 0°, 90°, and 180°. Both theoretical and practical periodic temperature boundary conditions are taken into consideration, in which the periodic temperature boundary conditions include 50-80 °C and 65-80 °C. The comparison study is carried out through the liquid fraction and temperature histories during the heat transfer process under these different boundary conditions. It is indicated that there are large differences between the calculated results under the theoretical and the practical periodic temperature boundary conditions when the temperature boundary is 50-80 °C, while the theoretical and the practical periodic temperature boundary conditions of 65-80 °C have relatively little effect on the numerical results of the heat transfer process of the phase change material. Furthermore, compared with the temperature increasing stage, the numerical results calculated under the theoretical and the practical boundary conditions have more significant differences in the temperature decreasing stage. The research conclusion of this paper can provide a theoretical basis for the application of phase change material under periodic temperature boundary conditions. [ABSTRACT FROM AUTHOR]

Phase change materials (PCMs) are recognized as a promising passive energy retrofit technology for existing buildings, as they are applied to the internal and external surfaces of the building with less impact on the original structure. However, the effectiveness of PCMs varies from region to region. Taking the Central Plains of China as an example, this paper investigated the effect of phase change temperature and material thickness variation on the energy efficiency of PCM when it was arranged on 14 placements including furniture through EnergyPlus (E+). And further explored the applicability of coupling PCMs with natural ventilation (NV). The results showed that: for the Central Plains of China, PCMs arranged on the internal surface of building roofs were optimal, and the reduction rate of uncomfortable degree hours could reach 38%, 26%, 24% and 40% after integrating PCMs into the roof, floor, external wall and furniture. The uncomfortable degree hour reduction rate per unit mass of PCM was 0.052%/kg for the roof, and the value of furniture was very close to the external wall and floor, which achieved 0.033%/kg. In addition, the coupling of PCM with NV improved the energy efficiency of PCM by more than twice. [ABSTRACT FROM AUTHOR]

Wood fiber is a great potential supportive material for creating a new composite the phase change materials (PCM) due to its beneficial qualities, including high sorption competency, low density, enviro -friendliness, economic effectiveness, and chemical inertness. The main objective of this paper is to study the effect of using the wood fiber/eutectic mixture of stearic and capric acid on the fuel, cost, and carbon emission-saving potentials for various PCM cases. Which experiences a phase transition within the thermally pleasant temperature range of buildings, used for the building's thermal energy storing purposes and consumption cost saving. The energy performance analysis was carried out for buildings incorporated with stearic and capric acid eutectic mixture of PCM with wood fiber-based insulation material (INS) in different climate regions. The results showed that the largest energy-saving capacity belongs to PCM5. The energy saving reaches 52.7% for PCM5 for a thickness of 0.1 m. The PCM1, PCM2, PCM3, PCM4 can provide energy saving rates of 23.5%, 34.3%, 44.7% and 50.5%, respectively. INS-PCM5 can provide about 1.74-, 1.5-, and 1.33 times larger cost savings than INS in 2nd, 3rd, and 4th regions for all fuels. The payback period varies between 0.37 and 5.81 years regarding the fuel and Region. Finally, the results indicate that the proposed composite provided a promising energy-saving potential in building applications by reducing. [ABSTRACT FROM AUTHOR]

This paper presents a thermokinetic computational model of phase transitions in GST225 (germanium–antimony–tellurium) thin films [as well as other phase change materials (PCMs)] induced and initiated by the impact of nano- and femtosecond laser pulses in a wide energy fluence range according to the results of experimental studies using Raman spectra and thin-film samples of TEM cross-sectional image analysis. Applying this phase transition model makes it possible to understand the mechanism of the induced phase transition regarding the usage of PCMs in photonics and optoelectronic devices, which require precise control of the phase state of their PCM-based active elements for their functioning. The proposed model shows the internal structure of the sample, generating both the profile of the crystalline fraction distribution over the sample's depth, providing images of virtual TEM sections, as well as the volume distribution of the crystalline phase. [ABSTRACT FROM AUTHOR]

Phase change materials are used in passive solar house construction with light steel structure walls, which can overcome the problems of weak heat storage capacity and poor utilization of solar heat and effectively solve the thermal defects of light steel structure walls. Based on this, on the basis of preliminary experimental research, this study further carried out theoretical analysis and simulation research on the thermal performance of a light steel structure passive solar house (Trombe form) with PCM walls. Through the heat balance analysis of heat transfer in the heat collecting partition wall, the theoretical calculation formula of the phase change temperature of the PCM was obtained, and it verified theoretically that the phase change temperature value should be 1–3 °C higher than the target indoor air temperature. The evaluation index "accumulated daily indoor temperature offset value" was proposed for evaluating the effect of phase change materials on the indoor temperature of the passive solar house, and "EnergyPlus" software was used to study the influence of the phase change temperature, the amount of material, and the thickness of the insulation layer on the indoor air temperature in a natural day. The results showed that there was a coupling relationship among the performance and between of the thickness of the PCM layer and the phase change temperature. Under typical diurnal climate conditions in the northern Tibetan Plateau of China, the optimal combination of the phase change temperature and the layer thickness was 17 °C and 15 mm, respectively. Especially at a certain temperature, excessive increases in the thickness of the phase transition layer could not improve the indoor thermal environment. For this transition temperature, there exists an optimal transition layer thickness. For a Trombe solar house, the thickness of the insulation layer has an independent impact on indoor temperature compared to other factors, which has an economic value, such as 50 mm in this case. In general, this paper studied the relationship between several important parameters of the phase change wall of a solar house by using numerical simulation methods and quantitatively calculated the optimal parameters under typical meteorological conditions, thus providing a feasible simulation design method for similar engineering applications. [ABSTRACT FROM AUTHOR]

Thermal control methods based on phase change materials have a wide range of applications, from thermal management to latent heat storage for renewable energy systems, with intermittent availability. Organic PCMs have some advantages over inorganics; however, their major drawback is flammability. In critical applications, such as buildings, electric vehicles, and aerospace applications, flammability is an issue that must be addressed in order to comply with safety standards. This review paper covers current studies assessing the PCM response to fire or excessive temperature, methods for ensuring flame retardancy, and their impact on the PCMs key characteristics: phase transition temperature range, latent heat, heat transfer rate, and compatibility with other system materials. A special focus is set on the preparation methods and the effectiveness of the flame-retardance achievement method. Some research gaps and further research directions are identified and discussed. [ABSTRACT FROM AUTHOR]

Phase change energy storage is a new type of energy storage technology that can improve energy utilization and achieve high efficiency and energy savings. Phase change hysteresis affects the utilization effect of phase change energy storage, and the influencing factors are unknown. In this paper, a low-temperature eutectic phase change material, CaCl2·6H2O-MgCl2·6H2O, was selected as the research object, combined with the mechanism of phase change hysteresis characteristics, using a temperature acquisition instrument to draw the step cooling curve. A differential scanning calorimeter was used to measure the DSC (differential scanning calorimetry) curve, and the hysteresis characteristics of phase transformation were studied by factors, such as heat storage temperature, cooling temperature, and cooling rate. The experimental results show that when heating temperature increases by 30 °C, phase transition hysteresis decreases by about 3 °C. The cooling temperature decreased by 10 °C, and the phase transition hysteresis increased by 2.69 °C. This paper provides a new idea for optimizing the properties of phase change energy storage materials and provides a possibility for realizing the parametric control of phase change hysteresis factors. [ABSTRACT FROM AUTHOR]

This paper showed two bio-based shape-stable composite phase change materials (PCMs) which were prepared through a convenient vacuum impregnation method. Lignin-based ordered porous carbon (LOC) was the porous supporting material, polyethylene glycol (PEG) and paraffin (PA) was the phase change substance in this work. The maximum loading of PCMs in the obtained LOC/PEG and LOC/PA are 70% and 75%, respectively, and their phase transition enthalpy (ΔHm) are also as high as 81.5 J·g−1 and 88.5 J·g−1, respectively. When the loading amount is the same as 60%, the thermal conductivity of LOC/PEG is 0.5029 W/mK, which is a 50.3% improvement over PEG. The thermal conductivity of pure PA is 0.3430 W/mK, and the thermal conductivity of LOC/PA is 0.5847 W/mK, an increase of 70.5% compared to paraffin. In addition, the obtained LOC/PA showed better thermal management capabilities and better thermal stability after infrared thermography tests compared to LOC/PEG. Considering the low cost and excellent properties, the obtained lignin-based ordered porous carbon composite phase change material has a promising future for practical applications in thermal energy storage. [ABSTRACT FROM AUTHOR]

Most of the studies investigated either charging or discharging process in a phase change material (PCM) based heat sink. In this paper, both melting and solidification of n-eicosane filled heat sink is studied numerically. The system filled only with PCM is unable to provide desired performance because of poor thermal conductivity of material. In order to enhance the response time, fins and foams are used in this study. Here, a PCM filled hybrid system of two cases is considered. For case 1, the heat sink with horizontal and vertical fins and for case 2, the heat sink with combination of horizontal fins and metal foams (aluminum) are employed. In case 1, no fin case is compared with rectangular fins and tapered fins. Results show that tapered fins are good for distribution of temperature within the system. In case 2, different filling heights such as 10 mm, 15 mm, and 20 mm with horizontal tapered fins are investigated. From the results, it is observed that the convection is delayed by increasing the filling heights. For solidification cases, 20 mm filling height foam performs better than all other cases. [ABSTRACT FROM AUTHOR]

Thermal management systems for lithium-ion batteries based on the cooling and heating of phase change materials have become a popular research topic. However, the low thermal conductivity, flame resistance, high and low temperature adaptability of phase change materials, as well as the thermal runaway mechanisms and lightweight design of phase change material-based systems remain to be explored. The aim of this paper is to conduct a publication-wide macro bibliometric review on thermal management systems for lithium-ion batteries based on phase change material to date. Total of 583 associated publications were retrieved from the Web of Science Core Collection database for the period 2006–2022. A bibliometric study was conducted through the visualization software VOSviewer. The findings were derived from annual publication trends, geographical and institutional distribution, authors and their collaborative networks, keyword network analysis and analysis of highly cited publications as well as reference co-citation analysis. The findings provide a comprehensive overview of the evolution of research hotspots in the field and can help researchers who would like to work in the field to quickly grasp the research frontiers and the overall picture. Furthermore, some suggestions for future work are summarized. [ABSTRACT FROM AUTHOR]

• A multi-parametric analysis study has been conducted for 96 building scenarios. • The impact of building construction on the energy and temperature performance is studied. • The effect of different phase change materials on temperature regulation is investigated. • Several configurations have been recommended for both building constructions. This paper presents a comparative study that will evaluate and optimize 96 building cases in a multi-parametric manner. This study is conducted by using the EnergyPlus simulation software with the integrated PCM hysteresis model. The studied building designs were carefully selected to have equivalent air volume, while taking into consideration the outer wall shape of the building to increase or decrease the outside sun and wind exposed surface as well as increasing the PCM area inside the buildings. Three different building forms were evaluated, the square form, the octagonal form which is considered as the building design with a reduced surface, and finally the innovative zigzag form which has a higher wall surface compared to the square form. Additionally, these three building forms, were evaluated at two different constructions (light-weight and heavy-weight), four different PCM types and four different HVAC scenarios. The main purpose of this study is to assess indoor air temperature fluctuation reduction, energy efficiency, and PCM activation. The results reveal an energy saving up to 13.1 % and a maximum total yearly temperature fluctuation reduction of 653 °C. The recommended building configuration was able to reach a maximum PCM activation of 26.63 %. [ABSTRACT FROM AUTHOR]

Latent heat thermal energy storage (LHTES) has received more and more attention in the thermal energy storage field due to the large heat storage density and nearly constant temperature during phase change process. However, the low thermal conductivity of phase change material (PCM) leads to poor performance of the LHTES system. In this paper, the research about heat transfer enhancement of PCM using fin tubes is summarized. Different kinds of fins, such as rectangular fin, annular fin, spiral fin, etc., are discussed and compared based on the shape of the fins. It is found that the longitudinal rectangular fins have excellent heat transfer performance and are easy to manufacture. The effect of fins on heat transfer enhancement is closely related to the number of fins and its geometric parameters. [ABSTRACT FROM AUTHOR]

One of the appealing technologies that contributes to raising the energy storage density is latent heat thermal energy storage. The heat of fusion is isothermally stored at a temperature representing the temperature at which a phase-change material transitions between phases. The current research provides a review of how phase transition materials are used in melting and solidification. Generally, the range of working temperature extends from -20°C to 200°C for solidification and melting applications. The first range (-20 to 5°C) is employed for commercial and domestic refrigeration. The second range (5 to 40 °C) is utilized to lower the energy requirements for air-conditioning applications. The applications includes in third range (40 to 82 °C) are solar collector and heating of water. Applications of absorption cooling, waste electricity generations, and heat recovery are operated at high temperature range (82 to180°C). There are various types of PCMs for all the above temperature ranges. The present review paper will discuss the application field, Geometry, PCM type, heat transfer augmentation technique and their effects on the performance. The conclusions are mentioned to give more insight about the PCM behavior in various applications. [ABSTRACT FROM AUTHOR]

This research paper describes the experimental investigation of the phase change characteristics of deionized (DI) water with the addition of functionalized graphene nanoplatelets (FGNP) in a spherical container used in cool thermal energy storage (CTES) systems. The nano-enhanced phase change materials (NEPCMs) are developed by the dissolution of FGNP in the mass concentrations of 0.25%, 0.50%, and 0.75% with DI water. The thermal conductivity (TC) and phase change enthalpy (H) of the NEPCMs were measured experimentally using the transient hot-wire method and DSC 214 polymer, respectively. At heat transfer fluid (HTF) temperatures of −10°C and 15°C, the mass fraction of 0.75 improves thermal conductivity by 48.2% and 33.2% in the solid and liquid phases, respectively. At a heating rate of 1K min-1, the addition of FGNP significantly reduces the H of the base PCM in both crystallization and melting processes. The maximum reduction in crystallization and melting time was recorded to be 32.4% and 52.4% in a spherical container with the addition of maximum concentration of FGNP at the HTF temperatures of −8°C and 25°C, respectively. [ABSTRACT FROM AUTHOR]

In this paper, a series of eutectic hydrated salts was obtained by mixing Na2HPO4·12H2O (DHPD) with K2HPO4·3H2O (DHPT) in different proportions. With the increase in the content of DHPT, the phase transition temperature and melting enthalpy of eutectic hydrated salts decreased gradually. Moreover, the addition of appropriate deionized water improved the thermal properties of eutectic hydrated salts. Colloidal silicon dioxide (SiO2) was selected as the support carrier to adsorb eutectic hydrated salts, and the maximum content of eutectic hydrated salts in composite PCMs was 70%. When the content of the nucleating agent (Na2SiO3·9H2O) was 5%, the supercooling degree of composite PCMs was reduced to the minimum of 1.2 °C. The SEM and FT-IR test results showed that SiO2 and eutectic hydrated salts were successfully combined, and no new substances were formed. When the content of DHPT was 3%, the phase transition temperature and melting enthalpy of composite PCMs were 26.5 °C and 145.3 J/g, respectively. The results of thermogravimetric analysis and heating–cooling cycling test proved that composite PCMs had good thermal reliability and stability. The application performance of composite PCMs in prefabricated temporary houses was investigated numerically. The results indicated that PCM panels greatly increased the Grade I thermal comfort hours and reduced energy consumption. Overall, the composite PCM has great development potential building energy conservation. [ABSTRACT FROM AUTHOR]

The paper studies the angle of incidence required to achieve minimal reflectance for p-polarization, referred to as the pseudo-Brewster angle, within the context of a phase change material. By using a thin-film material such as vanadium dioxide (VO 2), known for its phase transition from insulator to metal at 68 °C, which significantly alters the material's refractive indices, alongside an absorbing substrate like gold, we demonstrate the attainability of a pseudo-Brewster angle of zero. Moreover, this angle may be modulated by a wide margin during the phase transition. These findings are potentially interesting for balancing s- and p-polarizations and facilitating efficient control over light polarization properties. • Single interfaces cannot achieve zero-valued pseudo-Brewster angles (PBA). • Thin films can have zero-valued PBA in certain conditions. • VO2 is a phase-change material that undergoes significant changes in refractive indices during the phase transition. • We show that PBA modulation down to zero is possible in a VO2 thin film deposited on metals. [ABSTRACT FROM AUTHOR]

Vanadium dioxide reveals a phase change transition at 68 °C associated to typical hysteresis curves with strong variations in physico-chemical properties. The study presented here aims to investigate the influence of the structure and the microstructure of VO 2 condensed matter on optical transmittance and electrical resistivity hysteresis curves during the metal-insulator transition. The characteristics of VO 2 thin films synthesized through conventional laser ablation and of VO 2 nanoparticle stacks generated via a laser vaporization cluster source are investigated. This study reveals the capability to modulate the transition temperature by as much as 20 °C, the transition width within the range of 4–30 °C, and the resistivity dynamics across the semiconducting-to-metallic phase transition by more than two orders of magnitude. These effects appear to arise because of the change of microstructure, the physical percolation of nanoparticles and associated collective effects. More complex hysteresis behaviors, taking benefit of the fabrication processes presented in this paper, and coupling the two previous distinct VO 2 architectures (thin film and nanoparticles stack) lead to optical transmittance curves with three transition levels. This approach offers flexibility beyond binary responses, facilitating the design of innovative optoelectronic devices with n-stages modulation capabilities. Near room temperature applications of VO 2 metal-insulator transition are underscored, highlighting opportunities for tailored architectures to exploit its properties effectively. • 100 nm–200 nm of Vanadium dioxide thin films developed by pulsed laser deposition. • Collection of VO 2 nanoparticles synthesized by a laser vaporization cluster source free cluster generator. • Nanoparticle collective behaviors. • Transmittance and resistivity hysteresis width of up to 30 °C. • Complex architecture generating complex hysteresis curves at three levels. [ABSTRACT FROM AUTHOR]

With the integrated application of multiple detection technologies, multi-band compatible stealth is crucial to improve the counter-detection capability of targets. However, there are still significant challenges in achieving stealth that is compatible with different bands. This paper presents a wavelength-selective emitter with a structure consisting of a layer composed of a high-temperature-resistant material and a phase change material Ge 2 Sb 2 Te 5 (GST), and an upper truncated pyramid array composed of TiO 2. The structure can transition between "stealthy" and "non-stealthy" states by controlling the phase transition process of the GST. The structure in stealth mode has low reflectivity in the visible (VIS) region, low emissivity in the mid-wave infrared and long-wave infrared region. In addition, it has laser stealth at 1.06 μm and 1.54 μm, and provides radiative cooling in the non-atmospheric window (5–8 μm). The dipole resonance formed by TiO 2 on the side gives the structure lower reflectivity in the VIS band and at two laser wavelengths. The high emission in the non-atmospheric window is mainly attributed to the Fabry-Perot resonance supported in the structure. In addition, the effects of incidence angle and temperature on the stealth performance of the structure are investigated. This research has promising applications in the field of multi-band compatible stealth. • We propose a GST-based multi-band compatible stealth structure. • The structure can switch between "stealthy" and "non-stealthy" states. • This structure can realize stealth in the visible, infrared band and laser wavelength. • The structure achieves multi-band stealth at different angles and temperatures. [ABSTRACT FROM AUTHOR]

Annular thermoelectric power generator has been increasingly considered in application of ambient energy harvesting owing to the advantages of simple structure and no pollution. To improve thermal stability and energy harvesting performance of this system, the latent heat of phase change materials to improve thermal management and the high thermal conductivity of the heat sink to enhance heat transfer with the ambient are harness to annular thermoelectric power generator. Motivated by this, a phase change material based annular thermoelectric energy harvester (PCM-ATEH) with fins is developed for ambient energy harvesting and its three-dimensional transient model is also built up through jointly with thermo-electric and phase change processes. This paper considers the influence of key parameters such as temperature fluctuation amplitude, temperature fluctuation period, height ratio of PCM and thermoelectric generator (TEG) and melting temperature on liquid fraction, temperature difference, voltage and power density. Moreover, the comparison of PCM-ATEH and PCM based thermoelectric energy harvester (PCM-TEH) with/without fins is further conducted in this study to explore thermal management and energy harvesting performance. The energy harvesting characteristics of PCM-ATEH with fins is developed concerning the combination of power generation of TEG and melting process of PCM. Based on the results, it is found that the temperature difference and power density of PCM-ATEH with fins vary periodically with the sinusoidal temperature boundary, and results show that increasing temperature fluctuation period is not always feasible. Additionally, the comparative results indicate that the peak power density and energy efficiency of PCM-ATEH with fins are increased by 0.126 W/m2 and 0.02 % compared with PCM-TEH with fins, and increased by 0.195 W/m2 and 0.041 % compared with PCM-ATEH without fins. The results of energy harvesting characteristics show that a maximum of 0.77$ per watt can be reached to power generation cost of PCM-ATEH with fins. This paper can provide theoretical guidance for thermal management and energy conversion of energy harvesting system. [ABSTRACT FROM AUTHOR]

Annular thermoelectric power generator has been increasingly considered in application of ambient energy harvesting owing to the advantages of simple structure and no pollution. To improve thermal stability and energy harvesting performance of this system, the latent heat of phase change materials to improve thermal management and the high thermal conductivity of the heat sink to enhance heat transfer with the ambient are harness to annular thermoelectric power generator. Motivated by this, a phase change material based annular thermoelectric energy harvester (PCM-ATEH) with fins is developed for ambient energy harvesting and its three-dimensional transient model is also built up through jointly with thermo-electric and phase change processes. This paper considers the influence of key parameters such as temperature fluctuation amplitude, temperature fluctuation period, height ratio of PCM and thermoelectric generator (TEG) and melting temperature on liquid fraction, temperature difference, voltage and power density. Moreover, the comparison of PCM-ATEH and PCM based thermoelectric energy harvester (PCM-TEH) with/without fins is further conducted in this study to explore thermal management and energy harvesting performance. The energy harvesting characteristics of PCM-ATEH with fins is developed concerning the combination of power generation of TEG and melting process of PCM. Based on the results, it is found that the temperature difference and power density of PCM-ATEH with fins vary periodically with the sinusoidal temperature boundary, and results show that increasing temperature fluctuation period is not always feasible. Additionally, the comparative results indicate that the peak power density and energy efficiency of PCM-ATEH with fins are increased by 0.126 W/m2 and 0.02 % compared with PCM-TEH with fins, and increased by 0.195 W/m2 and 0.041 % compared with PCM-ATEH without fins. The results of energy harvesting characteristics show that a maximum of 0.77$ per watt can be reached to power generation cost of PCM-ATEH with fins. This paper can provide theoretical guidance for thermal management and energy conversion of energy harvesting system. [ABSTRACT FROM AUTHOR]

In order to study the micro behavior of alkanes and their interaction with carbon nanomaterials and metal nanomaterials in composite phase change materials (CPCM), in this paper, Cu surface and amorphous n-octadecane composite system (system A) and Cu surface, as well as graphene/n-octadecane composite system (system B), were constructed. The micro behavior of alkanes on the Cu surface was studied by molecular dynamics (MD) simulation. The MD results show that the alkane molecules are arranged in a relatively orderly crystalline form on the Cu surface because of the interface interaction and make the thermal conductivity of the alkane molecules in the composite system improved. Moreover, by comparing the self-diffusion coefficient of n-octadecane in these two systems, it is found that the phase transition temperature of n-octadecane in system A is about 300 K, while the phase transition temperature of n-octadecane/graphene composite system in system B is enhanced to 320 K. [ABSTRACT FROM AUTHOR]

A femtosecond laser could realize a high transition rate of the phase change material (PCM), and the properties of the amorphous and the crystalline Ge2Sb2Te5 (GST) induced by a femtosecond laser were studied, which was one of the candidates among the PCMs. However, the characteristics of the intermediate phase states in reversible phase transitions were also important and helpful to explore the mechanisms of the phase transitions. In this paper, the ultrafast dynamics of amorphous, crystalline face-centered-cubic (FCC), and hexagonal-close-packed (HCP) states were investigated using a femtosecond laser pulse excitation through a reflective-type pump–probe technique, obtained by annealing at certain temperatures, and verified using X-ray diffraction (XRD) and the Raman spectrum. It was found that as the annealing temperature increased, the electron of the GST films could be excited more easily, while the ablation threshold decreased. Due to annealing, the structure of bonding was changed for different phase states, which resulted in the decrease in the band gap of the films. In addition, it was hard for the intermediate state films to transit to the amorphous structure state via the femtosecond laser, and the crystallization would be enhanced, while the crystalline HCP structures of GST could be directly and easily changed to the amorphous state by a pulse, which resulted from the non-thermal phase change caused by the excited electron. [ABSTRACT FROM AUTHOR]

Phase Change Material (PCM) is mainly used in thermal energy storage. The addition of small PCM particles to the working fluid circulating in the heat exchange systems allowed to increase the amount of transported energy thanks to the use of latent heat—the heat of phase change. Encapsulating PCM in microcapsules avoids the disadvantages of PCM emulsions and makes the resulting slurry an attractive heat energy carrier. The paper presents the effect of the aggregate state of PCM enclosed in microcapsules on the flow resistance of the slurry through a rectilinear tubular channel. The tests were carried out with the use of a tube with an internal diameter of 4 mm and a measuring section length of 400 mm. A slurry of 21.5 wt.% PCM microcapsules (MPCM) was used as the working fluid in distilled water. A slurry with temperatures of 18.4 °C (PCM encapsulated in a solid state), 26.1 °C (PCM is in a phase change), and 30.5 °C (PCM in a liquid state) flowed through the measuring section. The mass flow rate of the MPCM slurry reached 70 kg/h (Remax = 2150). It was shown that the higher the Re number, the higher the value of the flow resistance, and the more clearly this value depended on the temperature of the slurry. Detailed analyses indicate that the observed changes were not the result of a change in the viscosity of the slurry, but its density depending on the state of the PCM. Significant changes in the density of the slurry in the range of the phase transition temperature are the result of significant changes in the volume of the microcapsule containing the phase change material in different aggregate states. [ABSTRACT FROM AUTHOR]

As a promising alternative to conventional heat transfer fluids, microencapsulated phase change material slurry (MPCS) was applied in ground heat exchanger (GHE) in this paper. A sandbox system embedded with horizontal serpentine GHE was installed and MPCS using N-eicosane (C 20 H 42) as phase change material is prepared. To explore the merits of MPCS, a comparison study between performance of water and MPCS was conducted. In addition, the enhanced heat transfer mechanism of MPCS were studied by comparing performance of MPCS with different inlet temperature and particle concentration. The experimental results indicate that the heat transfer rate and pumping consumption of 25 wt% MPCS with inlet temperature of 30 °C are 10.5 and 2.8 times that of water, respectively. The heat load-to-pumping consumption ratio has an enhancement of 3.73 times in comparison to water. Obviously, considering the phase transition process, MPCS can efficiently improve thermal performance of GHE. However, in the non-phase transition temperature range, the performance of MPCS is even worse than that of water. The comprehensive performance factor of 15 wt% MPCS and 25 wt% MPCS with inlet temperature of 38 °C declined by 45.6% and 36.9% in comparison with pure water. [ABSTRACT FROM AUTHOR]