Composite Phase Change Materials Research Articles

Novel composite phase change materials supported by oriented carbon fibers for solar thermal energy conversion and storage

Phase change materials (PCMs) have aroused significant interest as promising materials for solar thermal energy conversion and storage. However, the long-standing shortcomings of liquid leakage, low thermal conductivity, and weak solar absorptance limit their practical applications. Herein, novel composite phase change materials (CPCMs) with anisotropic heat conduction are manufactured by mixing continuous carbon fibers (CFs) and palmitic acid (PA)/olefin block copolymer (OBC) mixtures using pressure induction and vacuum treatment. Because the oriented CFs in the vertical direction can offer heat transfer channels inside the composites, the vertical and horizontal thermal conductivities of the CPCMs are 5.84 W·K−1·m−1 and 1.34 W·K−1·m−1, respectively, resulting in a relatively high anisotropic degree of 4.36. Furthermore, to improve the absorption of solar radiation for the composite, carbon black is applied to the upper surface of the CPCMs, achieving a high total solar absorptance of 0.966. Due to the combination of the high solar absorptance of the carbon black and the high vertical thermal conductivity within the composites, the CPCMs exhibit outstanding solar-to-thermal efficiencies of 87.54% ∼ 95.08% at 1– 3 kW·m−2. In addition, stability testing also confirms that the CPCMs have excellent leakage-proof properties, thermal stability, and cyclic stability for long-term utilization. This work can provide an efficient route to synthesize high-performance CPCMs for solar thermal applications.

Graphene nanoplatelets and copper foams for improving passive cooling performance of PCMs in Singapore's tropical climate

In Singapore's hot tropical climate, phase change materials (PCMs) hold significant promise for year-round passive cooling solutions in buildings. However, the narrow diurnal temperature range of 24–32 °C poses a great challenge for pure PCMs with poor thermal conductivity to undergo complete melting-freezing cycles. Herein, we tested two composite PCMs in a self-designed thermal box: (1) paraffin RT28HC/graphene nanoplatelets (GNP-PCMs) and (2) paraffin RT28HC/copper foam (CF-PCMs). The passive cooling performance of the composite PCMs was evaluated based on their charging power at 32 °C and discharging power at 24 °C. The focus is on convection heat transfer between the composite PCMs and ambient air, with considering various factors, including GNPs content (0.1–0.9 wt%), CF pore density (40 pores per inch (PPI) and 70 PPI), airflow rate (natural convection and forced convection), and orientation (horizontal and vertical). The results indicate that a minimum temperature range of 26.6–30.3 °C is necessary for complete melting-freezing cycles. The effect of GNPs content is more sensitive to orientation, whereas the effect of CF pore density is more affected by airflow rate. In all cases, the CF-PCMs exhibit superior temperature uniformity than the GNP-PCMs. Under forced convection, the charging power and discharging power of pure PCM reached a maximum of 110.8 and 163.5 W/m2, respectively. The addition of GNPs enhanced the charging power and discharging power of pure PCM by up to 14.2 % and 10.2 %, respectively. Moreover, the incorporation of CF boosted the charging power and discharging power of pure PCM by up to 75.1 % and 64.3 %, respectively.

Thermocapillary convection modes and phase change heat transfer characteristics of three-dimensional metal foam composited phase change materials with different aspect ratios under microgravity

This work aims to investigate the flow, heat transfer and phase change characteristics of porous media composite phase change materials with different aspect ratios in the thermocapillary mode under microgravity. A three-dimensional hydrodynamic model of thermocapillary-enhanced phase change heat transfer in the composite is developed. The model considers the shear stress boundary conditions on the porous free surface, employing the enthalpy-porosity method and the Darcy–Forchheimer model to describe the phase change process and fluid flow within the porous matrix, respectively, and the local thermal non-equilibrium model to describe the transient heat energy transfer between the paraffin and copper foam. The effects of different Marangoni numbers (Ma), aspect ratios (AR), Darcy numbers (Da) and porosities (ε) on the phase change heat transfer are compared. The results show that the increase of Ma from 6 × 104 to 2 × 105 accelerates the thermocapillary effect, and positively affect the thermal transport inside the cavity. The total melting time of the composite is reduced by 22.6 %, the heat storage efficiency is improved by 31.1 %, and secondary vortices appear in the convection zone. The large AR is favorable to the development of thermocapillary convection, but it also causes the reduced temperature gradient and heat transfer area of the heat source as well as the increased heat transfer distance. Compared to AR = 1, the total melting time increased by 34.4 % and 46.9 % for AR of 1.95 and 2.25 at a larger Ma, while the heat storage efficiency decreased by 26.5 % and 33.7 %, respectively. For a fixed ε, the decrease in Da hinders the development of convection, thus weakening the heat transfer and storage performance of the composite, and also causes heat conduction to dominate the phase change process in advance.

Performance analysis and comparison study of liquid cooling-based shell-and-tube battery thermal management systems

To meet the temperature control requirements of lithium-ion batteries (LIBs) under high rate discharge conditions, this study designed two structurally similar shell-and-tube battery thermal management (BTM) schemes, namely air-cooled/liquid cooled coupling scheme and phase change material (PCM)/liquid cooled coupling scheme. By applying simulation methods to analyze and compare the battery temperature control performance of two schemes under different working conditions, and adopting structural optimization and heat dissipation strategies to decrease the maximum temperature and temperature difference of the battery. It can be concluded that the maximum temperature of the batteries in both cooling schemes remains below 333 K after the number of baffle plates is increased from 2 to 6 during 5C discharge. Among them, the PCM/liquid cooling scheme demonstrates superior temperature control capabilities. However, the air cooling/liquid cooling scheme can also effectively reduce the temperature difference of the battery pack to 4.7 K by frequently switching the ventilation direction. The temperature difference of the battery can be further reduced by enhancing the thermal conductivity of composite phase change materials (CPCM). It is worth noting that increasing the liquid cooling flow rate to 2.5 m/s no longer improves the cooling effect of the battery. Additionally, during each discharge stage of cyclic charging and discharging, intermittently turning off the water pump for 9 min results in the battery exhibiting favorable temperature cycling characteristics.

From waste to value: Utilising waste foundry sand in thermal energy storage as a matrix material in composites

Waste foundry sand (WFS) is a by-product of the casting industry, which poses increasing economic and environmental issues due to the costs associated with landfill maintenance and stricter environmental regulations. This study proposes a novel solution for WFS as a material for thermal energy storage. The approach involves blending WFS with NaNO3 and a proprietary additive, X, to fabricate a composite phase change material (CPCM). The CPCM is found to be structurally stable up to 400 °C, and an optimal composition with a mass ratio of NaNO3:WFS:X = 0.6:0.3:0.1 is achieved. This composition yields an energy storage density of 628 ± 27 kJ/kg, and an average thermal conductivity of 1.38 W/mK over the temperature range of 25–400 °C. The CPCM also exhibits good mechanical strength and a low coefficient of thermal expansion compared to NaNO3. Currently, only a small portion of WFS is recycled, most commonly in building applications. The CPCM presented in this study has the potential for medium-to-high temperature heat storage in waste heat recovery applications, offering a sustainable solution for upcycling WFS.

Influence mechanism of battery thermal management with flexible flame retardant composite phase change materials by temperature aging

The phase change immigration of flame retardant Composite Phase Change Material (CPCM), especially the temperature aging effect during multicycle process, greatly restricted its application in power battery pack of electric vehicle and energy storage system. In this study, the properties of flexible flame-retardant CPCMs before and after temperature aging were investigated, and the battery thermal management effects of battery modules were compared. The results revealed that flexible CPCMs with styrene block copolymers exhibited little volume change owing to their elastic and anti-leakage properties, effectively alleviating flow and agglomeration. In addition, battery modules with flexible flame-retardant CPCMs exhibited prominent battery thermal management. These mechanisms in flame-retardant CPCMs can profoundly affect the design and preparation of multifunction CPCMs, providing novel insights into passive thermal management of battery systems.

Cellulose nanocrystal stabilized copper nanoparticles for grafting phase change materials with high thermal conductivity

Phase change materials (PCMs) have recently garnered significant attention for thermal energy storage applications. However, widely used PCMs, such as polyethylene glycol (PEG), suffer from low heat conductivity, poor thermal stability, and a tendency to leak, limiting their practical use. Therefore, the objective of this study is to develop a highly thermally conductive composite PCM using PEG and a thermally conductive nanomaterial, specifically cellulose nanocrystals supported by copper nanoparticles (CNC@Cu-NPs). The CNC@Cu-NPs nanocomposite material was used as a matrix to support polyethylene glycol (PEG), resulting in a shape-stable phase change material termed PEG/CNC@Cu-NPs. The obtained PEG/CNC@Cu-NPs were characterized using various analytical techniques. Fourier transform infrared spectroscopy (FTIR) analysis revealed the chemical linkages between PEG and cellulose nanocrystals through a radical polymerization reaction. Polarizing optical microscopy (POM) images of PEG/CNC@Cu-NPs exhibited spherocrystal morphology with smaller sizes compared to pure PEG, suggesting that CNC inhibited PEG side-chain mobility. According to differential scanning calorimetry, the suggested PEG/CNC@Cu-NPs demonstrated a temperature transition between 0.51 °C to 24.5 °C with enthalpies of fusion and crystallization measured at 92.19 and 98.54 J/g, respectively, while also exhibiting excellent cycling stability after 60 heating/cooling cycles. The addition of a modest amount of copper nanoparticles resulted in a remarkable improvement (>50 %) in the thermal conductivity of the PCM. Thermal imaging using an infrared camera showed that PEG/CNC@Cu-NPs exhibited a delay of 10 min in heating compared to pure CNC, confirming the good heat retention capacity of the developed composite material. Based on the aforementioned findings, the proposed PEG/CNC@Cu-NPs PCM offers promising application possibilities in the field of thermal energy storage.

Converting bio-waste rice into ultralight hierarchical porous carbon to pack polyethylene glycol for multifunctional applications: Experiment and molecular dynamics simulations

A structural-functional integrated shape-stabilized composite phase change material (PCM) was synthesized by converting biowaste rice into ultralight (0.08 g/cm3) hierarchical porous carbon (CNR) to pack polyethylene glycol (PEG) PCM. The thermal property and corresponding mechanism were analyzed. The results show that the composite PCM exhibits excellent thermal storage efficiency (93.3 %), considerable solar photothermal conversion efficiency and superior thermal stability. The interfacial thermal resistance (ITR) of PEG/CNR is 73 % lower than graphene foam-based composite PCM thus a fast transient temperature response. Particularly, the package of PEG endowed composite PCM with elastic characteristic thereby an enhanced compressive strength. Furthermore, covering PEG/CNR results in a delay of approximately 1.3 times in reaching the peak temperature on the surface of electronic components, and a delay of 5 times in cooling time. This study presents solid guidelines for societal development that is sustainable and makes some recommendations for construction of composite PCMs combining multifunctional applications.

Double-layered phase change materials featuring high photothermal conversion for stable thermoelectric power generation

Organic solid-liquid phase change materials have attracted great attention in the field of photothermal conversion and energy storage due to their advantages such as high latent heat, low subcooling, stable chemical properties, and constant temperature during the phase change process. However, preparing organic composite phase change materials (CPCMs) with multiple desirable properties such as good shape stability, high thermal conductivity, high enthalpy, and excellent photothermal conversion efficiency, remains a challenge. Herein, using a rapid melt blending of expanded graphite (EG) into lauric acid (LA) and cold pressing technique, we constructed double-layered and shape-stabilized D-LA/EG composites. The upper layer consists of 20 wt% EG and 80 wt% LA, while the lower layer 6 wt% EG and 94 wt% LA. It was found that the prepared D-LA/EG exhibited good shape stability, high thermal conductivity, high enthalpy, and excellent photothermal conversion efficiency. More interestingly, when applied as a heat source for an all-solid-state thermoelectric generator in a photo-thermal-electric conversion system, a stable output voltage of 315 mV is generated after the light is ceased, which is attributed to the release of the heat stored in the CPCMs. This work provides a simple and economical strategy to synthesize and balance the above four properties CPCMs, which has potential applications in photo-thermal-electric conversion and solar energy utilization.

Enhanced thermal storage and photo-thermal conversion composite phase change materials based on MOF-derived carbon for efficient solar energy utilization

Composite phase change materials (PCMs) with high thermal conductivity and photo-thermal conversion performance can be employed for the efficient conversion and utilization of solar energy. In this work, a Ni-doped carbon material derived from a Ni metal-organic framework (Ni-BTC) is prepared and used as the supporting material to encapsulate polyethylene glycol (PEG). The Ni-BTC derived carbon (NBC) obtained retained the intrinsic porous flower-like structure which facilitates the encapsulation of PEG. The doping of Ni metal particles enhances both the thermal conductivity and photo-thermal conversion performance of the composite PCM. Additionally, the thermal conductivity of the composite PCM is further enhanced by the addition of a graphene/Ag composite, resulting in a thermal conductivity that is 3.15 times higher than that of pure PEG. The latent heat of the resulting composite PCM is 125.4 J/g, the photo-thermal conversion efficiency is 91.81 %. Moreover, the composite PCM exhibits excellent thermal stability and reliability, indicating its potential for wide-ranging applications in solar energy storage.

Experimental study of phase transition heat of composite thermal energy storage materials paraffin wax/expanded graphite

In this paper, the effect of the expanded graphite (EG) matrix on the phase transitions enthalpy of phase change material (PCM) is studied experimentally. For this purpose, the paraffin wax (PW) containing EG (up to 6.5 wt%) was explored in terms of the effective heat capacity and a diffuse phase transitions enthalpy difference over the 25–65 °С temperature range. Composite PCMs PW/EG was prepared using a new method and were inherent in high pores fill factor. The main advantage of the proposed method is preliminary vacuuming of the PW and EG with subsequent mixing and sonication under vacuum. The EG choice was based on the hypothesis that the EG matrix contributes to modifying the PW internal structure due to the PW molecules' adsorption on the EG surface during PCM cooling and solidification. Consequently, a significant change in PW/EG caloric properties vs. pure PW was observed. The EG presence in PW reverses the enthalpy hysteresis in the heating-cooling cycle vs. pure PW. The enthalpy difference during PW heating and melting in the range of 30–60 °С is higher than during its cooling and solidification: 336.2 J∙g−1 vs. 214.9 J∙g−1. On the contrary, the enthalpy difference of melting for PW/EG of 3.6 wt% in the range 30–60 °С was 171.2 J∙g−1 vs. 273.8 J∙g−1 during solidification. The obtained results are explained by the different dynamics of processes of PW melting and solidification in EG matrix pores. The presence of the 3.2–6.5 wt% of EG in PW contributes to an increase in solidification enthalpy difference in the range 30–60 °C on 27–33 % vs. pure PW. A decrease in the melting enthalpy difference for PW/EG on 44–50 % vs. pure PW was recorded in the range of 30–60 °C. In addition, thermal conductivity was measured to confirm the advantages of PW/EG as PCM. Thermal conductivity for PW/EG with EG content of 3.6 and 6.5 wt% at 25 °C was 8.9 and 9.6 times higher than for pure PW. Similarly, 8.8 and 10.9 times thermal conductivity increase was observed at 65 °C. The composite PCM containing 3.6 wt% of EG in PW obtained by developed method can be recommended as a rational composition in benefit of the thermal conductivity and caloric properties for utilization in high-performance TES systems.

A comprehensive review of the thermal performance in energy efficient building envelope incorporated with phase change materials

As the world's largest energy consumer, the building sector is under growing pressure to reduce energy consumption and CO2 emissions. To confront this challenge, the thermal performance of building elements, especially for cooling purposes, must be enhanced. One promising solution involves the incorporation of PCMs to augment a building's thermal mass. Unlike traditional building materials that store thermal energy sensibly, PCMs store it in a latent form by undergoing phase transitions at constant temperatures. This unique characteristic allows PCMs to store and release more heat efficiently than sensible heat thermal energy storage materials. As a result, PCMs have emerged as a prominent solution for passive cooling and heating applications in buildings. This paper proposes a systematic review of existing literature, classifying it based on building components and effective PCM integration methods while considering climatic influences. The primary objective is to comprehensively analyze the application of PCMs within building envelopes to enhance indoor thermal comfort. This study explores various methods for assessing the thermal properties of PCMs and PCM composites. Notably, integrating PCMs into building components like walls and roofs has shown remarkable potential in reducing energy consumption within the building envelope. This approach is precious in lightweight construction, where conventional passive design strategies may fall short. This study aims to bridge the existing research gap and provide valuable insights for designing energy-efficient buildings across diverse climates by systematically evaluating the impact of directly incorporating thermal energy storage systems into building components.

Experimental investigation on the freeze-thaw durability of a phase change concrete in cold regions

In cold regions, freeze-thaw induced damage to concrete is among the most severe issues that affect structures, leading to shortened lifespans of concrete-related structures and causing substantial economic losses. Therefore, it is crucial to enhance the freeze-thaw durability in cold regions. To achieve this aim, we combined n-tetradecane (C14) and expanded perlite (EP) to produce a composite phase change material (EPC14) with cement encapsulation. The essential material performances of the EPC14 were characterized through a series of physical and chemical tests. The measurement results show that the EPC14 possesses an appropriate phase change temperature, chemical stability, and mechanical reliability. Hence, it is an excellent candidate material for producing phase change concrete. In this study, we selected five volumetric replacement ratios of the EPC14 to fine aggregates (0%, 10%, 20%, 30%, and 40%) to prepare the phase change concretes (PCC-EPC14s). After these PCC-EPC14s samples were properly cured and then underwent 0, 50, 100, and 200 freeze-thaw cycles (FTCs), their physical and mechanical properties were systematically measured through nuclear magnetic resonance (NMR), resonance frequency tests, and uniaxial compression tests. The comprehensive measurement results demonstrate that at 0 FTCs, a higher content of the EPC14 results in larger porosity in the PCC-EPC14s, leading to lower compressive strength and relative dynamic modulus of elasticity. However, after 200 FTCs, the PCC-EPC14 (20%) exhibits the highest compressive strength and relative dynamic modulus of elasticity, whereas the PCC-EPC14 (0%) exhibits the lowest values for both of these properties. Furthermore, fractal theory was employed to analyze the mechanical properties of the PCC-EPC14s from a microscopic perspective. The results indicate that the PCC-EPC14 (20%) exhibits the largest NMR fractal dimension after 200 FTCs, signifying the least complexity and integration in its pore structure. In comparison to the PCC-EPC14s (0%, 10%, 30%, 40%), it is less prone to developing damage cracks under compression. In conclusion, we advise using the PCC-EPC14 (20%) in practical construction projects. The PCC-EPC14s prepared in this paper offer valuable insights for enhancing the freeze-thaw durability of concrete in cold regions.

An in-situ growth Fe3O4 and polyaniline on carbon cloth encapsulated composite phase change materials with high thermal conductivity and photothermal energy conversion and storage

Phase change materials (PCMs) play a crucial role in thermal management and solar energy utilization. However, PCMs suffer from low thermal conductivity, tend to leak during the phase change process, and do not possess photothermal conversion properties, limiting their application in these fields. In this work, thermally conductive enhanced composite PCMs with photothermal conversion are fabricated by encapsulating polyethylene glycol (PEG) into Fe3O4 and polyaniline (PANI) decorated carbon cloth (CC). The prepared PEG@PFCC composite PCMs exhibited high heat storage density (132.06–137.25 J/g), significantly improved leakage-proof properties, and excellent thermal and cyclic stability. Meanwhile, the continuous double-coating of PANI and Fe3O4 not only gives the composite PCMs superb thermal conductivity (thermal conductivity of 1.61 W/m·K, 416 % higher than that of the pristine PEG), but also high photothermal conversion efficiency (91.5 %) and excellent electromagnetic interference (EMI) shielding (up to 38 dB), which broaden the composite PCMs' adaptability of applications. In summary, this innovative type of carbon cloth-based composite PCMs provide a creative path for the design and development of energy storage and conversion materials, which exhibit tremendous potential in the applications of electronic protection, infrared stealth, thermal management of wearable devices, and solar thermal energy utilization.

Experimental and numerical investigation on the cold harvest of composite phase change materials for building energy conservation

This paper investigates the cold energy storage of a horizontal shell-tube latent heat thermal energy storage (LHTES) unit for the cold harvest during night time. An experimental apparatus containing a horizontal circular tube with circumferential heating/cooling was designed and developed. Paraffin based phase change material (PCM) with a melting temperature of 27 °C was adopted as the cold harvest media. To improve the heat transfer rate, multi-walled carbon nanotubes (MWCNTs) were mixed with the paraffin to form a composite PCM with high thermal conductivity. A corresponding model of the composite PCM was developed and verified against the experimental data. Numerical simulations were performed for different boundary temperatures and concentrations of MWCNTs. The results show that when the heat transfer temperature difference is 20 °C, 0.05 wt% nanoparticles increase the melting rate of PCMs. When the heat transfer temperature difference was 40 °C, 0.10 wt% nanoparticles significantly affect the PCM melting rate. For low or high temperature (heat transfer temperature difference of 10 °C and 80 °C), the addition of nanoparticles is not conducive to improving the melting rate.

Ground tire rubber/activated carbon/expanded graphite aerogels and foams as support material for the preparation of polyethylene glycol composite phase change materials for thermal energy storage applications

The 3 “Rs” of trash management, reduce, reuse, and recycle, lead to a theoretical topic. Techniques for waste management should reprocess these waste products into new functional materials. In the area of thermal energy storage, phase change material (PCM) is another hot topic due to its high latent heat. Unfortunately, it is constrained by issues such as simple leakage and poor heat conductivity. Herein, we integrate waste material and phase change material by preparing composite phase change material in which aerogels and foams serve as 3D support matrices that were made using ground tire rubber, activated carbon and expanded graphite additives to successfully overcome the aforementioned disadvantages of phase change material via Porogen leaching and freeze drying techniques. Experiment findings demonstrated that the CPCM has excellent shape stability. TAA5 and TAE5 had the highest melting enthalpies, at 146.21 and 148.23 J/g respectively. After 500 thermal test cycles and 25 photothermal test cycles, the prepared CPCMs exhibit strong thermal reliability as evidenced by a small decrease in enthalpy value. In addition, the thermal conductivity of TAE15 was remarkable at 1.18 W/(mK), which was 5.36 times greater than that of PEG 0.22 W/(mK). The use of AC and EG as additives boosted TAE15's photothermal conversion efficiency to 93 %. Hence, CPCMs offer a significant deal of potential in fields such as thermal energy storage, solar energy, and building energy savings.

MXene-modified bio-based pitaya peel foam/polyethylene glycol composite phase change material with excellent photo-thermal conversion efficiency, thermal energy storage capacity and thermal conductivity

The preparation of multifunctional composite phase change materials (CPCM) for efficient conversion and storage of solar energy using green technology remains a big issue. Herein, in this research, a novel CPCM was prepared for the first time by encapsulating polyethylene glycol (PEG) into MXene-modified pitaya peel-based porous carbon using a simple vacuum impregnation method. Pitaya peel-based porous carbon was selected as the carrier to coat with MXene nanosheets to construct a continuous three-dimensional thermal conductivity network. The MXene-modified bio-based pitaya peel foam/polyethylene glycol composite phase-change material (PEG/BPC@M) exhibited high loading ratio (95.4 %) and enthalpy (154.9 J/g). Interestingly, due to the introduction of MXene nanosheets, both the photothermal conversion (θ = 92.9 %) and thermal conductivity (2.34 times that of PEG) of PEG/BPC@M were substantially increased. Significantly, PEG/BPC@M with outstanding thermal stability, wherein the PEG/BPC@M still maintained enthalpy values similar to those in non-thermal cycles after 100 cycles, further proving that PEG/BPC@M has outstanding reusability. This study provided a simple and green novel process for the preparation of multifunctional CPCM, similarly, it provided a feasible scheme for waste reuse, which has huge potentials for the field of solar energy conversion and storage.

Form-Stable Composite Phase Change Materials Based on Porous Copper-Graphene Heterostructures for Solar Thermal Energy Conversion and Storage.

Solar-thermal energy conversion and storage technology has attracted great interest in the past few decades. Phase change materials (PCMs), by storing and releasing solar energy, are able to effectively address the imbalance between energy supply and demand, but they still have the disadvantage of low thermal conductivity and leakage problems. In this work, new form-stable solar thermal storage materials by impregnating paraffin PCMs within porous copper-graphene (G-Cu) heterostructures were designed, which integrated high thermal conductivity, high solar energy absorption, and anti-leakage properties. In this new structure, graphene can directly absorb and store solar energy in the paraffin PCMs by means of phase change heat transfer. The porous structure provided good heat conduction, and the large surface area increased the loading capacity of solar thermal storage materials. The small pores and superhydrophobic surfaces of the modified porous G-Cu heterostructures effectively hindered the leakage issues during the phase change process. The experimental results exhibited that the thermal conductivity of the prepared form-stable PCM composites was up to 2.99 W/(m·K), and no leakage took place in the solar-thermal charging process. At last, we demonstrated that the PCM composites as an energy source were easily integrated with a thermoelectric chip to generate electric energy by absorbing and converting solar energy.

Synthesis and characterization of Capric acid-Lauric acid/expanded vermiculite as a phase change composite for thermal energy storage

In this study, a new kind of composite phase change material (PCM) using expanded vermiculite (EVM) as the matrix and Capric acid-Lauric acid (CA-LA) binary eutectic as the adsorbent was fabricated by vacuum impregnation technology. The devised composite CA-LA/EVM with 60 % loadage of CA-LA and melts at 18.42 °C with a latent heat of 66.08 J/g. In addition, in order to investigate whether the prepared composite CA-LA/EVM can be used in building envelope for energy conservation, we mixed it as heat regulating medium to prepare the phase change concrete, the mechanical, thermal performance, failure patterns and stress concentration of CA-LA/EVM-based phase change concrete was studied systematically. The results indicate that incorporating CA-LA/EVM into concrete can observably enhance the specific heat capacity and heat storage capacity of concrete. It is important to emphasize that the failure cracks in CA-LA/EVM-based concrete mainly extend along the interface between CA-LA/EVM and cement slurry, the effect of axial strain on the strength of CA-LA/EVM-based phase change concrete has been noted to be particularly significant.

A novel bio-based composite phase change material with excellent photo-thermal conversion capability for solar energy harvesting and energy storage

Organic solid-liquid phase change materials (PCMs) have been widely studied in the field of photo-thermal conversion and thermal energy storage. However, problems such as easy leakage and low efficiency of photo-thermal conversion limit their applications. To solve these problems, this study developed a shape-stable composite phase change material (CPCM) using sponge tissue of discarded corn stem (STCS), polyethylene glycol (PEG), pyrrole (Py), and multi-walled carbon nanotube (MWCNT). PPy and MWCNT enable the CPCM to have excellent photo-thermal conversion capability and thermal conductivity. With 0.2 % MWCNT content, the CPCM achieved a thermal conductivity of 0.4609 W/m·K and a photo-thermal conversion efficiency exceeding 95.3 %. It also demonstrated high enthalpy and relative enthalpy efficiency (152.2 J/g, 96.01 %). Moreover, the CPCM exhibited remarkable shape and thermal stability, with no pyrolysis below 340 °C and nearly unchanged enthalpy after 100 cycles. Meanwhile, this CPCM also showed excellent ability in promoting seawater desalination. This work provides a new idea for recycling of agricultural waste and storage of solar energy as well as desalination of seawater.