Heat Storage Capability Research Articles

High‐Performance Infrared Scene Generation Using a Double‐S Microbridge Photothermal Film Emitter With Ultralarge Array

AbstractInfrared emitters are highly desirable for applications in infrared imaging and stealth technology. Photothermal film emitters, which are driven by light, have garnered considerable interest due to their excellent photothermal properties and ease of fabrication. However, existing photothermal films often suffer from low photothermal conversion efficiency (PCE) and limited array scale. Here, a photothermal film emitter featuring a double‐S microbridge structure is presented, which comprehensively considering the PCE and frame rate. Initially, Si microbridges are fabricated within each microstructure to support the photothermal film. The pattern structure is then arranged into a double‐S configuration to manipulate the thermal conductivity. By optimizing the length and width of the double‐S pattern, high PCE and fast frame rates are achieved. The double‐S microbridge structure photothermal film emitter is fabricated with a 4‐inch diameter, forming an ultra‐large array with over 3000 × 3000 pixels. The absorption and photothermal conversion characteristics are studied, revealing a maximum temperature of 582.70 K and a highest PCE of 16.32%. Time‐dependent photothermal response demonstrated the emitter's rapid heat storage and release capabilities. Additionally, an infrared scene generator is realized. These results position the photothermal film emitter as a promising solution for infrared imaging and dynamic scene generation.

Hybrid membranes incorporating microencapsulated PCM for enhanced hygrothermal performance in enthalpy recovery ventilation systems

Advancements in building technologies are increasingly centered on improving energy efficiency, particularly within ventilation systems. Integrating Microencapsulated Phase Change Materials (MPCMs) into paper-based membranes enhances hygrothermal performance in enthalpy recovery ventilation systems. MPCMs, known for their latent heat storage capabilities, were incorporated at concentrations of 0 %, 5 %, 10 %, and 20 % by weight. The hybrid membranes exhibited a significant latent heat storage capacity, achieving up to 34.38 J/g at MPCM 20 wt% content. Although the latent heat decreased by approximately 10 % after 1000 cycles of extreme temperature fluctuations between 15 °C and 60 °C, the membranes still exhibited durability sufficient to endure a replacement cycle of over three years, maintaining their effectiveness in long-term applications. The addition of MPCMs also led to improvements in moisture resistance, with the moisture resistance coefficient increasing from 8.88 to 19.19 at MPCM 20 wt%, while still preserving sufficient moisture permeability for efficient enthalpy exchange. These improvements in thermal and hygrothermal properties underscore the potential of MPCM-integrated membranes to enhance energy efficiency and thermal comfort in HVAC systems, providing a sustainable solution for modern building designs. The findings suggest further exploration into optimizing MPCM content for varying climate conditions and assessing the long-term performance of these membranes in diverse practical applications.

State of the art on solid–gas sorption based long-term thermochemical energy storage

Solid-gas sorption thermochemical heat storage technology is an innovative and promising solution for storing heat over long periods. The review focuses on the construction of composite sorption thermochemical heat storage materials and binary mixed salt materials with porous matrix as the supporting materials, which can further improve the hydration rate and cycle stability of single hydrated salt. Furthermore, the heat storage capabilities of the metal halide/ammonia working pair make it suitable for extreme environments, surpassing the limitations of water-based working pairs in terms of low-temperature adaptability. It is worth noting that common solid–gas reactors and measures to enhance heat and mass transfer are also reviewed. Meanwhile, the efficient open and closed heat storage systems and their optimization schemes are introduced, and the feasibility of the practical operation of the heat storage systems is evaluated comprehensively from the technical and economic perspectives, and the future research challenges are prospected.

Material-level experimental study on utilising ionic liquid/graphene composites for sorption heat storage

Sorption heat storage technology has recently sparked an increasing interest because of its advanced heat storage capabilities. However, material-level heat and mass transfer challenges persist. This work contributes to the field by the development of new sorption composite materials that are comprised ionic liquids (1-ethyl-3-methylimidazolium methanesulfonate and 1-ethyl-3-methylimidazolium chloride) impregnated in 1–5 2D-layered graphene host matrix. Their sorption, heat transfer, heat storage, and charging/discharging rate properties were experimentally investigated using both water and ethanol as adsorbates. The adsorption isotherms and kinetics for both the adsorbates onto the developed composites and the parent ionic liquids were experimentally measured at different temperatures. The isosteric heat of adsorption for all the studied pairs was determined using the Clausius-Clapeyron method, showing an increasing trend with an increasing uptake. They showed that the specific heat storage capacity reached 187.5 kJ/kg when water was used as the working sorption agent. The corresponding heat charging/discharging rates are significantly higher, 69 %-78 %, than pure ionic liquids. Compared to silica gel as a baseline sorbent, ionic liquid-graphene composites’ heat storage and transfer capacities are higher by three orders of magnitude. The thermal diffusivities of the developed composites were significantly higher than the baseline silica gel. These innovative sorption composites show great potential for improving thermal energy storage efficiency, making them suitable for applications in renewable energy systems, industrial processes, waste heat recovery, and climate control solutions. However, the developed composites achieved inferior performance compared to the silica gel baseline sorbent when using ethanol as a working fluid to utilise sub-zero ambient air as a heat source because of the relatively larger molecular size of ethanol.

A unique solar pond system integrated with chlor-alkali electrolyser for heat storage and hydrogen production

Solar ponds are recognized as a simple, but a unique solution for renewable heat storage to use later. A freshwater feed to solar ponds is considered a crucial requirement to maintain the salinity gradient accordingly for heat storage purposes. This study aims to benefit from this specific requirement for solar ponds by integrating chlor-alkali electrolysers to produce hydrogen along with heat storage, which is a common purpose of a solar pond. Therefore, the proposed system establishes a desirable synergy, as per the sustainable development goals, between a conventional solar pond and an innovative high-tech hydrogen production system. In order to produce hydrogen, the saline water withdrawn from the upper convective zone is used in a chlor-alkali electrolyser powered by solar PV in order to produce green hydrogen. Thus, a conventional solar pond is converted into an integrated energy system that produces hydrogen and chlorine for useful purposes, along with heat storage capability. The system’s performance has been assessed in terms of the energy and exergy efficiencies for five distinct cities located in different countries that are grappling with poverty. The system’s performance, which is assessed in five cities, demonstrates the energy and exergy efficiencies ranging from 11.66 % to 14.56 % and 6.84 % to 8.60 % for the solar pond. They vary from 21.95 % to 24.22 % and from 14.23 % to 14.66 % for the overall system, respectively. Furthermore, the system effectively captures and stores solar energy, and it reaches temperatures up to 89.1°C. Moreover, the proposed system is expected to contribute to the United Nations’ Sustainable Development Goals by addressing energy poverty, promoting clean energy, and fostering economic growth.

A novel solar-driven thermogalvanic cell with integrated heat storage capabilities

Low-grade heat sources like solar thermal radiation offer a vast energy resource. However, their low utilization rate limits energy recovery and conversion efficiency. Solar thermogalvanic cells, utilizing solar thermal radiation as a heat source, are considered an effective way to harness solar energy. However, their widespread application is hindered by performance instability due to periodic solar radiation fluctuations. This study developed composite electrodes with high conductivity, excellent photothermal properties, and heat storage capabilities, and applied them in thermogalvanic cells. Compared to traditional thermal chemical cells, the new heat storage electrode materials significantly enhance the stability and energy output efficiency. The results show that under temperature fluctuations, the new thermal chemical cells (EG/SA/LA-TGCs) significantly improve power output stability. The temperature difference increased from 6 °C to 17 °C, with the open-circuit voltage rising to 32 mV. Thanks to the electrodes’ heat storage and release capability, the heat released by the electrodes sustains the cell’s power generation. The discharge duration per unit volume of the electrode reached 12.74 min/cm3, 15 times longer than traditional thermal chemical cells.

Green building material with superior thermal insulation and energy storage properties fabricated by Paraffin and foam cement composite

In the field of architecture and construction, foam cement has been gradually gaining popularity due to its outstanding attributes of reduced weight, carbon footprint, and potential thermal insulation effects. However, relying solely on the thermal insulation provided by the foam in foam cement lacks the capability to store and release heat. In this paper, a novel approach is proposed by directly incorporating paraffin into foam cement with non-continuous pores, creating a phase change foam cement. The addition of paraffin to foam cement, facilitated by the presence of surfactants in foam, allows the paraffin to disperse. In contrast, if paraffin is directly added to cement without the foam, it tends to aggregate. The internal pore structure, thermal performance, phase change temperature, and relaxation distributions were investigated through equipment such as scanning electron microscope (SEM), thermal conductivity meter, differential scanning calorimetry (DSC), and H1 nuclear magnetic resonance (NMR). Results indicate that paraffin/foam cement plays a dual function, effectively storing and releasing energy, significantly enhancing its thermal insulation performance. Particularly, the incorporation of 10 vol% paraffin content results in a notable 21.8 % reduction in the thermal conductivity, for foam cement with a density of 600 kg/m3. This is attributed to the heat storage capability of the phase-change paraffin, which absorbs heat as the surrounding temperature rises, synergistically collaborating with the foam. This presents a novel perspective for the development of green and energy-efficient building materials, contributing to the realization of sustainable energy utilization in the construction industry.

Ultrathin aerogel-structured micro/nanofiber metafabric via dual air-gelation synthesis for self-sustainable heating

Incorporating passive heating structures into personal thermal management technologies could effectively mitigate the escalating energy crisis. However, current passive heating materials struggle to balance thickness and insulating capability, resulting in compromised comfort, space efficiency, and limited thermoregulatory performance. Here, a dual air-gelation strategy, is developed to directly synthesize ultrathin and self-sustainable heating metafabric with 3D dual-network structure during electrospinning. Controlling the interactions among polymer, solvent, and water enables the microphase separation of charged jets, while adjusting the distribution of carbon black nanoparticles within charged fluids to form fibrous networks composed of interlaced aerogel micro/nanofibers with heat storage capabilities. With a low thickness of 0.18 mm, the integrated metafabric exhibits exceptional thermal insulation performance (15.8 mW m−1K−1), superhydrophobicity, enhanced mechanical properties, and high breathability while maintaining self-sustainable radiative heating ability (long-lasting warming of 8.8 °C). This strategy provides rich possibilities to develop advanced fibrous materials for smart textiles and thermal management.

High reflectivity and latent heat synergetic TiO2/Cs0.33WO3-PU double-layer materials with zero transmittance

Passive Cooling Technology, as a method of achieving long-term refrigeration without the need for external energy input, has emerged as an alternative to traditional energy-intensive cooling, garnering increasing attention from academia and industry. However, current passive cooling technology faces challenges such as incomplete solar energy reflection, overcooling, and inevitable absorption of solar radiation and surrounding environmental heat. This paper presents a passive cooling bilayer film with latent heat storage capability, composed of a solid–solid phase change polyurethane (PU) matrix with added TiO2 and Cs0.33WO3.TiO2/Cs0.33WO3-PU exhibits minimal solar transmittance, with reflectance and emissivity rates of 84.46 % and 93.08 %, respectively. The solid–solid phase change matrix effectively mitigates overcooling and heat input issues, reducing temperature fluctuations and peaks, and thereby enhancing passive cooling performance. At the phase transition temperature (306 K), TiO2/Cs0.33WO3-PU achieves cooling powers of 113.77 W/m2(day time) and 173.19 W/m2(night time), the temperature can be reduced by 14.3 °C under 100 mW/cm2sunlight. Additionally, TiO2/Cs0.33WO3-PU demonstrates outstanding thermal stability and reliabitity, hydrophobicity, as well as resistance to UV aging. Moreover, it offers the flexibility to adjust the phase transition temperature and latent heat of the solid–solid phase change matrix according to specific environmental conditions. TiO2/Cs0.33WO3-PU combines passive cooling materials with phase change materials, and complements each other’s advantages. TiO2/Cs0.33WO3-PU not only improves the cooling power, but also provides a new solution to the problem of heat input and supercooling of passive cooling materials. TiO2/Cs0.33WO3-PU also provides new possibilities for the application of passive cooling materials in the fields of long-term outdoor building cooling, human heat management, food preservation and electrical equipment cooling.

Bio-based composite phase change material utilizing wood fiber and coconut oil for thermal management in building envelopes

Bio-based materials are attracting substantial attention for their eco-friendly attributes within the construction field, where they facilitate energy saving and emissions reduction. However, the performance of it, such as thermal properties, needs to be improved. Fully utilizing bio-based materials, we developed a novel composite phase change material (PCM), A-WF/CO/h-BN, with high thermal storage properties designed for application in building envelopes. It incorporates coconut oil (CO) as the PCM featuring an optimal phase change temperature. Hexagonal boron nitride (h-BN) was chosen to enhance the thermal conductivity. Acetylated wood fiber (A-WF) was employed as the supporting material. The prepared A-WF/CO/h-BN sample exhibits excellent and rapid heat storage and exothermic capabilities. In the experiment of thermal performance evaluation, the cold end of the A-WF/CO/h-BN sample is cooler than that of the A-WF when both hot ends are heated. Results indicate that the proposed A-WF/CO/h-BN sample can effectively delay the heat transfer and inhibit the temperature rise and fall. For these superior properties, when the A-WF/CO/h-BN sample is applied in building envelopes, it can minimize the heat transfer from the envelope to the interior and inhibit indoor temperature fluctuation. Thus, it can reduce building energy consumption and carbon emissions while achieving indoor thermal comfort.

Enhancing visible light absorption of form-stable CH3COONa·3H2O composite phase change material and its application in thermoelectric power generation

The utilization of Phase Change Material (PCM) for solar heat storage represents an effective solar energy storage method. Nevertheless, this promising technology encounters several obstacles, particularly PCM leakage and dissatisfied solar absorptance. This study focuses on the development of a photothermal conversion composite PCM tailored for solar energy storage and its subsequent integration into a thermoelectric power generation system. The composite PCM was synthesized using an evaporation-impregnation method, with melamine foam (MF) serving as the adsorbent material, graphene oxide (GO) as the light-absorbing component, and sodium acetate trihydrate (SAT) as the thermal storage medium. It is shown that the MF demonstrates an exceptional adsorption capacity for SAT, whose mass fraction exceeds 99 % in the final composite. The composite PCM exhibits a remarkable melting enthalpy of 251.5 J/g, comparable to that of pure SAT. The integration of GO into MF/SAT improves the solar absorptance of the composite, elevating it from 23.3 % to 81.5 %, thereby enhancing the photothermal conversion performance. To assess the practical solar energy storage potential of the prepared PCM, a thermoelectric power generation system was designed and underwent a continuous 22-hour performance test in a real outdoor enviornment. The results reveal that the system is able to maintain voltage generation for about 10 hours after the sun disappears. This proves the superior photothermal conversion and heat storage capabilities of the prepared materials. This research offers a viable approach for direct solar energy storage and conversion to electricity, advancing renewable energy technologies.

A novel biogenic porous core/shell-based shape-stabilized phase change material for building energy saving

The application of phase change materials (PCMs) for thermal storage in construction can effectively reduce building energy consumption. However, high costs and vulnerability to leaks have hindered their application. The present study proposes two approaches for the synthesis of porous supporting matrices derived from rice husk, resulting in the formation of rice husk silica (RHS) and rice husk carbon (RHC). Then, n-octadecane and the porous materials were combined by vacuum impregnation, while the leakage resistance performance of the composite PCMs was enhanced by applying epoxy resin coating to create a shell-core structure. The results show that the n-octadecane/RHS and n-octadecane/RHC composite PCMs exhibit high latent heat potential of 106.5 J/g and 116.3 J/g, respectively. Both porous supporting structures provided the PCMs with robust structural stability and exceptional thermal conductivity. The thermal conductivity of the n-octadecane/RHS composite PCMs and n-octadecane/RHC composite PCMs reached 0.52 W/(m K) and 0.41 W/(m K), respectively. The thermal properties of the biogenic porous core/shell-based shape-stabilized PCMs were characterized by an analog T-history method, and the results demonstrated that the composite PCMs exhibited excellent and rapid heat storage and exothermic capabilities. After undergoing 300 complete heating and cooling cycles, the composite PCMs demonstrate exceptional thermal reliability and possess a high enthalpy capacity. Finally, the impact of the pore structure of RHS and RHC on the crystallization behavior of n-octadecane was discussed. Both composite PCMs can be regarded as environmentally friendly construction materials with promising thermal and acoustic properties.

Poly(ethylene glycol)-based polyurethanes based on dynamic oxime-urethane bonds for sustainable thermal energy storage

Traditional poly(ethylene glycol)-based polyurethane phase change materials (PUPCMs) are difficult to reprocess and non-recyclable because of their permanently cross-linking structure, leading to issues of resource waste. To overcome this problem, this study introduces dynamic bonds in PUPCMs to develop dynamic cross-linking networks. A series of polyurethane phase change materials containing dynamic oxime-urethane bonds (DOU-PUPCMs) are prepared using poly(ethylene glycol) (PEG), dimethylglyoxime (DMG) and hexamethylene diisocyanate (HDI) as raw materials. It has been shown that the obtained DOU-PUPCMs exhibit good heat storage capability and outstanding thermal stability. Importantly, the introduction of oxime-urethane groups provided DOU-PUPCMs with processibility. After multiple reprocessing cycles, the chemical structure and energy storage capacity of the DOU-PUPCMs essentially remain consistent with the original samples. The breaking and restructuring of oxime-urethane bonds and hydrogen bonds in DOU-PUPCMs makes them recyclable. This is not only significant for the development of recyclable and sustainable energy storage materials, but also complements studies such as the application of oxime-urethane bonds to PCMs.

Development of Macro-Encapsulated Phase-Change Material Using Composite of NaCl-Al2O3 with Characteristics of Self-Standing

Developing thermal storage materials is crucial for the efficient recovery of thermal energy. Salt-based phase-change materials have been widely studied. Despite their high thermal storage density and low cost, they still face issues such as low thermal conductivity and easy leaks. Therefore, a new type of NaCl-Al2O3@SiC@Al2O3 macrocapsule was developed to address these drawbacks, and it exhibited excellent rapid heat storage and release capabilities and was extremely stable, significantly reducing the risk of leakage at high temperatures for industrial waste heat recovery and in concentrated solar power systems above 800 °C. Thermal storage macrocapsules consisted of a double-layer encapsulation of silicon carbide and alumina and a self-standing core of NaCl-Al2O3. After enduring over 1000 h at a high temperature of 850 °C, the encapsulated phase-change material exhibited an extremely low weight loss rate of less than 5% compared with NaCl@Al2O3 and NaCl-Al2O3@Al2O3 macrocapsules, for which the weight loss rate was reduced by 25% and 10%, respectively, proving their excellent leakage prevention. The SiC powder layer, serving as an intermediate coating, further prevented leakage, while the use of Al2O3 ceramics for encapsulation enhanced the overall mechanical strength. It was innovatively discovered that the Al2O3 particles formed a network structure around the molten NaCl, playing an important role in maintaining the shape and preventing leakage of the composite thermal storage phase-change material. Furthermore, the addition of Al2O3 significantly enhanced the rapid heat storage and release rate of NaCl-Al2O3 compared to pure NaCl. This encapsulated phase-change material demonstrated outstanding durability and rapid heat storage and release performance, offering an innovative approach to the application of salt phase-change materials in the field of high temperature rapid heat storage and release and encapsulating NaCl as a high-temperature thermal storage material in a packed bed system. Compared with conventional salt-based phase-change materials, the developed product is expected to significantly improve the reliability and thermal efficiency of thermal storage systems.

Enhancing Thermal Energy Storage: Investigating the Use of Graphene Nanoplatelets in Phase Change Materials for Sustainable Applications

The adoption of phase change materials (PCMs) for thermal energy storage in low‐ and medium‐temperature settings is witnessing a notable surge. However, the lesser thermal conductivity (TC) poses a noteworthy challenge to PCM's heat transfer and storage capabilities. One of the noteworthy solutions to augment the TC is incorporating nanoparticles in the PCM. Nevertheless, nanoparticles often clump together after several cycles due to poor compatibility and weak interfacial strength. Functionalization methods have been proposed to address this issue, offering improved performance for energy storage applications. Herein, graphene nanoplatelets (GNP) and functionalized graphene nanoplatelets (FGNP) are dispersed into A70 PCM at mass fractions ranging from 0.1 to 1.0 wt% using two‐step method. Fourier transform infrared analysis confirms the successful integration of FGNP into A70 PCM without altering its chemical characteristics. Adding 1.0 wt% FGNP to A70 PCM increases its TC by 140.88%, with just a 3.02% decrease in latent heat enthalpy. However, incorporating pure GNP (1.0 wt%) improves TC by 48.83%. The engineered nano‐PCMs exhibit robust thermal and chemical stability even after undergoing 1000 thermal cycles, remaining unchanged up to 414.64 °C. This exceptional stability makes the formulated nanoenhanced PCM suitable for sustainable thermal applications.

Enhancing Building Energy Efficiency: Leaf Transpiration Inspired Construction of Lignin-Based Wood Plastic Composites for Building Energy Conservation

Incorporating phase change materials (PCMs) into buildings represents a strategic method for reducing reliance on air conditioning systems and decreasing energy usage consequently. Inspired by leaf veins providing channels for transpiration, lignin porous carbon (LPC) was synthesized by chemical activation, showing a vein pore structure. The capillary network system of the LPC provided more channel to adsorb PCM through surface tension and capillary force, achieving an impressive loading capacity of LPC for polyethylene glycol (PEG) (75%), which demonstrated exceptional heat storage capability (133.21 J/g). The lignin-derived wood-plastic composite (L-WPC) was further prepared. With the gradual increase of LPC/PEG, the latent heat of L-WPC increased gradually. The ΔHm, ΔHc and energy storage efficiency of L-WPC-50 (incorporated 50 wt% LPC/PEG-75) reached 39.99 J/g, 42.65 J/g and 90.26%, respectively. The vein pore structure of LPC also provided a thermal conductivity link for L-WPC. L-WPC-50 demonstrated an increased thermal conductivity (0.66 W/(m·K)) and a reduced thermal diffusion coefficient (0.24 mm2/s), optimizing the effectiveness of the phase transition. Additionally, L-WPC-50 displayed satisfactory mechanical properties and dimensional stability, with tensile strength, bending modulus and water absorption thickness swelling rate measuring 14.40 MPa, 1043.72 MPa, and 1.61% respectively. It introduced a feasible approach for utilizing biomass in enhancing building energy efficiency, marking a significant stride towards reducing building energy consumption and advocating sustainable energy practices.

Highly flexible composite phase-change material PA-EG-AgNPs achieved through self-assembly of nano-silver for enhanced photothermal performance

This study presents an innovative composite phase-change material (cPCM) based on paraffin-expanded graphite (PA-EG), where AgNPs self-assemble onto the PA-EG surface. In comparison with the base material, the resulting composite, PA-EG12Ag-G, achieves a notably elevated thermal conductivity of 2.987 W/(m·K), emphasizing its superior heat conduction. Remarkably, the photothermal conversion efficiency sees a significant boost of 20.1 %, underlining its enhanced capacity for converting light to heat, attributed to the surface plasmon resonance of AgNPs. The cPCM also features a substantial phase change enthalpy of 130.5 J/g, ensuring exceptional heat storage capability. With a phase transition temperature of 46.3 °C, it gives multiple-choice for applications. Moreover, the material maintains outstanding room-temperature flexibility, making it being well-suited for practical use, such as a thermal management or solar thermal energy storage. The improvement in photothermal efficiency, facilitated by the surface plasmon resonance of AgNPs, adds a novel dimension to the material's capabilities, enhancing its potential for diverse applications.

Phase Change Nanocapsules Enabling Dual-Mode Thermal Management for Fast-Charging Lithium-Ion Batteries.

The fast-charging performance of conventional lithium-ion batteries (LIBs) is determined by the working temperature. LIBs may fail to work under harsh conditions, especially in the low-temperature range of the local environment or in the high-temperature circumstances resulting from the release of substantial Joule heating in the short term. Constructing a thermal engineering framework for thermal regulation and maintaining the battery running at an appropriate temperature range are feasible strategies for developing temperature-tolerant, fast-charging LIBs. In this work, we prepare phase change nanocapsules as a thermal regulating layer on the cell surface. The polyurea shells of the nanocapsules are decorated with polyaniline, where the molecular vibration of polyaniline is enhanced under solar irradiation, enabling light-to-heat conversion that achieves an effective temperature increment at low temperatures. Based on the large latent heat storage capability of the n-octadecane core in the nanocapsules, the thermal regulating layer is sufficient to modulate strong heat release when operating LIBs at a high current rate, which efficiently prevents strong side reactions at high temperatures or even the occurrence of thermal runaway. This work highlights the promise of optimizing the operating temperature with a thermal regulator to ensure the safety and performance stability of fast-charging LIBs.

Heat-Transfer Properties of Additively Manufactured Aluminum Lattice Structures in Combination with Phase Change Material.

Compared to sensible heat storage, latent heat storage provides higher energy density due to the enthalpy difference of the storage medium undergoing a phase change. However, the heat storage capability of phase change materials is opposed by low thermal conductivity. To enable sufficient heat transfer within a latent heat storage unit, phase change materials can be used in combination with a metallic matrix. One approach is the infiltration of phase change materials into additively manufactured metallic lattice structures. In this work, the fabrication of aluminum lattice structures through laser powder bed fusion is described. During fabrication, the cell size and the strut diameter were varied to obtain specimens of different geometries. To obtain the thermal conductivity of the fabricated lattices, measurements were conducted based on the transient plane source method. Additionally, finite element simulations were carried out to evaluate the effect of fabrication and measurement uncertainties. The thermal conductivity of the fabricated lattices was found to be between 3 W/(m·K) and 130 W/(m·K). The numerically and analytically performed calculations provide good estimations of the experimentally obtained data.

Passive dimming phase change material inspired by polymer hydrogels

As a new concept of smart materials, passive dimming phase change materials (PDPCMs) have potential in the field of energy-efficient buildings due to ultra-high energy utilization efficiency. Novel PDPCMs materials are reported by simulating the microstructure of high light transmittance polymer hydrogels. The self-prepared composite coordinates the inherent contradiction between anti liquid leakage, optical transmittance switching, and thermal storage density. There is an interaction between the hydroxyl groups (–OH) of MA and the ester groups (–COOR) of polybutylmethacrylate (PBMA), resulting in the PBMA/MA with a VMA/VPBMA volume ratio of 6:5 exhibiting good resistance to liquid leakage even when stretched to about 400 % at 60 °C. Based on the good compatibility and well-matched refractive index between MA and PBMA framework materials, the visible light transmittance of as-prepared PDPCMs has increased from 0.1 % at 30 °C to 89.0 % at 60 °C. The as-prepared composite also exhibits a good latent heat-storage capability with satisfactory phase-change enthalpies of over 113 J g−1. The as-prepared PDPCMs eliminate the spatial positional differences between photo-thermal conversion and thermal energy absorption, without considering the thermal conductivity of PDPCMs. The photo-thermal conversion efficiency can be increased by introducing well-matched color changing ink (CCI), significantly improving energy utilization efficiency. On the other hand, energy-saving doors/windows containing PBMA/MA composite materials allow sunlight to spread indoors due to the high transmittance (89.0 %) at high temperatures. The new design concept makes passive dimming composite materials suitable for high latitude areas.