Microfluidic Fabrication and Thermal Properties of Microencapsulated N-Hexadecane with a Hybrid Polymer Shell for Thermal Energy Storage

In this study, a strategy based on microfluidic method is developed toward a facile fabrication of phase change material microcapsules with uniform and controllable particle size as well as high encapsulation ratio and thermal stability. N-hexadecane, as a phase change material, was successfully encapsulated by a hybrid shell of poly (methyl methacrylate) and polyurea. The fabrication process includes the following three steps: (1) Formation of oil-in-water droplets with uniform micron size in the microfluidic chip; (2) formation of the first polyurea shell to encapsulate droplets by fast interfacial polymerization when the droplets pass through the coiled transport microchannel; and (3) completion of free radical polymerization of methyl methacrylate inside the microspheres by heating to form the hybrid microcapsule shell. The average size, encapsulation ratio, and phase change enthalpy of microcapsules changed by varying the flow rate of the dispersion phase and raw material composition. The highest melting enthalpy of 222.6 J g⁻¹ and encapsulation ratio of 94.5% of the microcapsule were obtained when the flow rates of the continuous and dispersion fluids were 600 μL min⁻¹ and 24 μL min⁻¹, respectively. It is shown that the phase change material microcapsules were stable after 50 heating/cooling cycles.     

Thermal Characterization of Medium-Temperature Phase Change Materials (PCMs) for Thermal Energy Storage Using the T-History Method

To reduce energy consumption and increase energy efficiency in the building sector, thermal energy storage with phase change materials (PCMs) is used. The knowledge of the thermophysical properties and the characteristics of PCMs (like their enthalpy changes and the distribution of stored energy over a specified temperature range) is essential for proper selection of the PCM and optimal design of the latent thermal energy store (LHTES). This paper presents experimental tests of the thermophysical properties of three medium-temperature PCMs: OM65, OM55, RT55, which can be used in domestic hot water installations and heating systems. Self-made test chambers with temperature control using Peltier cells were used to perform measurements according to the T-history method. In this way the temperature range of the phase transition, latent heat, specific heat capacity, enthalpy and the distributions of stored energy of the three PCMs were determined. The paper also presents measurements of the thermal conductivity of these PCMs in liquid and solid state using a self-made pipe Poensgen apparatus. The presented experimental tests results are in good agreement with the manufacturers’ data and the results of other researchers obtained with the use of specialized instruments. The presented research results are intended to help designers in the selection of the right PCM for the future LHTES co-working with renewable energy systems, waste heat recovery systems and building heating systems.     

Preparation of Stable Phase Change Material Emulsions for Thermal Energy Storage and Thermal Management Applications: A Review

Thermal energy storage (TES) is an important means for the conservation and efficient utilization of excessive and renewable energy. With a much higher thermal storage capacity, latent heat storage (LHS) may be more efficient than sensible heat storage. Phase change materials (PCMs) are the essential storage media for LHS. PCM emulsions have been developed for LHS in flow systems, which act as both heat transfer and thermal storage media with enhanced heat transfer, low pumping power, and high thermal storage capacity. However, two major barriers to the application of PCM emulsions are their instability and high degree of supercooling. To overcome these, various strategies have been attempted, such as the reduction of emulsion droplet size, addition of nucleating agents, and optimization of the formulation. To the best of our knowledge, however, there is still a lack of review articles on fabrication methods for PCM emulsions or their latest applications. This review was to provide an up-to-date and comprehensive summary on the effective strategies and the underlying mechanisms for the preparation of stable PCM emulsions and reduction of supercooling, especially with the organic PCMs of paraffin. It was also to share our insightful perspectives on further development and potential applications of PCM emulsions for efficient energy storage.     

Study on Influencing Factors of Phase Transition Hysteresis in the Phase Change Energy Storage

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.     

Effect and Mechanism of Polyethylene Glycol (PEG) Used as a Phase Change Composite on Cement Paste

The use of phase change materials (PCMs) in the construction industry is one of the primary strategies for addressing the building industry’s present excessive energy usage. However, since PCMs must be enclosed before being used in construction, their efficiency is limited and their compatibility with concrete is poor. Thus, polyethylene glycol (PEG), a sequence of PCMs that may be put directly into concrete, is the target of this research. The fluidity, mechanical properties, thermal properties, hydration process, and hydration products of PEG-600 cement slurry were examined by TAM, XRD, FTIR, DSC, MALDI, etc., methods in this study. Furthermore, we tested the thermal properties of PEG-800 to confirm that the same depolymerization of PEG occurred in an alkaline environment. When PEG, with a molecular weight of 600 (PEG-600), dose was increased to 10%, both compressive and flexural strength fell by 19% and 18%, respectively. The phase change points of both PEG-600 cement paste and PEG-800 cement paste decreased to 10~15 °C, and the enthalpy of the phase change was about 6 J/g. Additionally, it was discovered that PEG entered the reaction during the hydration step. PEG underwent depolymerization and subsequently formed a complex with Ca²⁺. However, due to the large dose of PEG used in this investigation, a self-curing effect of PEG in concrete was not seen. The findings of this research suggest a novel use for PCMs: PEG may be directly applied to concrete to fulfill both mechanical and thermal requirements. Additionally, the number of hydration products and phase compositions remained almost constant.     

Design of Eutectic Hydrated Salt Composite Phase Change Material with Cement for Thermal Energy Regulation of Buildings

An energy-efficient eutectic hydrated salt phase change material based on sodium carbonate decahydrate and disodium hydrogen phosphate dodecahydrate (SD) was prepared. Then, SD was encapsulated into expanded graphite (EG) to produce form-stable composite phase change materials (SD/E), which indicated a positive effect on preventing the leakage of SD, decreasing the supercooling and improving the thermal conductivity. SD/E was further tested for thermal efficiency by simulating the indoor environment with a house-like model which was composed of SD/E and magnesium oxychloride cement. The results showed an excellent thermal insulation effect. This exciting porous composite phase shift material reveals possible architectural applications because of the attractive thermos-physical properties of SD/E.     

Characterization and Reliability of Caprylic Acid-Stearyl Alcohol Binary Mixture as Phase Change Material for a Cold Energy Storage System

This study reports the in-depth investigation of the thermophysical properties and thermal reliability of caprylic acid-stearyl alcohol (CA-SA) eutectic phase change material (PCM) for cooling applications. The phase diagram of CA-SA showed a eutectic point at a 90:10 molar ratio. The onset melting/freezing temperature and latent heat of fusion of caprylic acid-stearyl alcohol from the differential scanning calorimetry (DSC) were 11.4 °C/11.8 °C and 154.4/150.5 J/g, respectively. The thermal conductivity for the prepared eutectic PCM in the solid phase was 0.267 W/m.K (0 °C), whereas, in the liquid phase, it was 0.165 W/m.K (20 °C). In addition, the maximum relative percentage difference (RPD) marked at the end of 200 thermal cycles was 5.2% for onset melting temperature and 18.9% for phase change enthalpy. The Fourier transform infrared spectroscopy (FT-IR) result shows that the eutectic PCM holds good chemical stability. Corrosion tests showed that caprylic acid-stearyl alcohol could be a potential candidate for cold thermal energy storage applications.     

Microencapsulated Phase Change Material Suspension for Cold Start of PEMFC

We added microencapsulated phase change materials (MPCMs) into the homemade antifreeze fluid to take advantage of the latent heat of phase change materials, and explored the possibility of solving the cold start problem of proton exchange membrane fuel cells (PEMFC) with variable specific heat capacity antifreeze. The physical and chemical properties of the MPCMs and their suspensions were tested, and a PEMFC platform for cold start with a thermal management system was established to compare the exothermic performance of MPCS and commercial antifreeze fluid. According to the output voltage, temperature and polarization curves before and after cold start, the MPCMs has a stronger heat transfer capacity than the commercial antifreeze fluid, and the addition of MPCMs can transform the latent heat generated during the phase transition into apparent specific heat capacity, leading to a better solution to the problem of PEMFC cold start.     

Experimental Study on the Development of Fly Ash Foam Concrete Containing Phase Change Materials (PCMs)

Phase change materials (PCMs) have the ability to absorb and release a large amount of energy during the process of transforming physical properties (i.e., phase transition process). PCMs are suitable for thermal energy storage and reducing energy consumption in buildings. The aim of the study is to assess the basic material properties and thermal behavior of fly ash foam concrete mixed with two different types of microencapsulated PCMs (PCM6D and PCM18D). We made five different varieties of fly ash foam concrete by replacing the equivalent unit weight of cement with PCM 0%, PCM 10% and PCM 30%. The results show that using a new type of mixer, the microencapsulated PCMs kept their spherical shapes without any cracks or damage in the foam concrete matrix. Differential scanning calorimetry analysis showed that PCM18D-30% had a latent heat capacity of 19.2 °C and 44.7 J/g, in liquid and solid phase with melting and freezing temperatures of 9.46 °C and 41.7 J/g respectively. Additionally, thermocycle analysis showed that it had maintained the temperature for 8 h within the phase change range. In conclusion, PCMs can reduce indoor temperature fluctuations and exhibit the potential for enhancing energy savings and thermal comfort of buildings.     

Mechanical,Thermal, and Fire Properties of Composite Materials Based on Gypsum and PCM

One of the solutions for overheating the interior in the summer without increasing energy consumption is the integration of phase change material (PCM) into interior plasters. However, adding PCM to plasters deteriorates their properties and thus their usability. The aim of this paper is to determine how the microencapsulated PCM affects the mechanical, thermal, and fire properties of plasters and how much PCM can be added to the plaster. Two sets of samples were prepared: in set S, part of the aggregate was replaced by PCM; and in set R, only PCM was added. The bulk density, flexural strength, compressive strength, tensile strength perpendicular to the surface, thermal conductivity coefficient, specific heat capacity, melting, and solidification temperatures and enthalpy were measured. A single-flame source fire test and a gross heat of combustion fire test were performed to determine the reaction to the fire class. The results show that with an increasing proportion of PCM, the strength of the samples of set R decreased more significantly than it did with the samples of set S. It was found that only up to about 10% PCM could be added to set R, while up to 30% PCM could be added to set S.     

Enhanced Thermal Performance of Composite Phase Change Materials Based on Hybrid Graphene Aerogels for Thermal Energy Storage

Thermal conductivity and latent heat are crucial performance parameters for phase change materials (PCMs) in thermal energy storage. To enhance the thermal performance of PCMs, with the help of graphene oxide (GO) acting as a dispersing agent, well-defined hybrid graphene aerogels (HGAs) with a three-dimensional (3D) porous structure were successfully synthesized by hydrothermal reaction of GO and graphene nanoplatelets (GNPs). GNPs, dispersing uniformly along the interconnecting graphene network, acted as thermal conductive fillers and supporting materials. Palmitic acid (PA) was impregnated into the HGA by vacuum forces. It was found that the thermal conductivity of the PA/HGA was enhanced without compromising heat storage capacity. Compared with PA, the PA/HGA with 4.2 wt% GNPs exhibited enhanced thermal conductivity of 2.1 W/mK and high latent heat of 206.2 J/g simultaneously. The PA/HGA with good thermal performance has potential applications in thermal energy storage.     

In-Situ Reaction Method to Synthetize Constant Solid-State Composites as Phase Change Materials for Thermal Energy Storage

The encapsulation and heat conduction of molten salt are very important for its application in heat storage systems. The general practice is to solidify molten salt with ceramic substrate and enhance heat conduction with carbon materials, but the cycle stability is not ideal. For this reason, it is of practical significance to study heat storage materials with a carbon-free thermal conductive adsorption framework. In this paper, the in-situ reaction method was employed to synthetize the constant solid-state composites for high-temperature thermal energy storage. AlN is hydrolyzed and calcined to form h-Al₂O₃ with a mesoporous structure to prevent the leakage of molten eutectic salt at high temperature. Its excellent thermal conductivity simultaneously improves the thermal conductivity of the composites. It is found that 15CPCMs prepared with 15% water addition have the best thermal conductivity (4.928 W/m·K) and mechanical strength (30.2 MPa). The enthalpy and the thermal storage density of 15CPCMs are 201.4 J/g and 1113.6 J/g, respectively. Due to the excellent leak-proof ability and lack of carbon materials, the 15CPCMs can maintain almost no mass loss after 50 cycles. These results indicate that 15CPCMs have promising prospects in thermal storage applications.     

Preparation of Colored Microcapsule Phase Change Materials with Colored SiO2 Shell for Thermal Energy Storage and Their Application in Latex Paint Coating

This article reports the design and manufacture of colored microcapsules with specific functions and their application in architectural interior wall coating. Utilizing reactive dyes grafted SiO₂ shell to encapsulate paraffin through interfacial polymerization and chemical grafting methods, this experiment successfully synthesized paraffin@SiO₂ colored microcapsules. The observations of surface morphology demonstrated that the colored microcapsules had a regular spherical morphology and a well-defined core-shell structure. The analysis of XRD and FT-IR confirmed the presence of amorphous SiO₂ shell and the grafting reactive dyes, and the paraffin possessed high crystallinity. Compared with pristine paraffin, the thermal conductivity of paraffin@SiO₂ colored microcapsules was significantly enhanced. The results of DSC revealed that the paraffin@SiO₂ colored microcapsules performed high encapsulation efficiency and desirable latent heat storage capability. Besides, the examinations of UV-vis and TGA showed that the paraffin@SiO₂ colored microcapsules exhibited good thermal reliability, thermal stability, and UV protection property. The analysis of infrared imaging indicated that the prepared latex paint exhibited remarkable temperature-regulated property. Compared with normal interior wall coatings, the temperature was reduced by about 2.5 °C. With such incomparable features, the paraffin@SiO₂ colored microcapsules not only appeared well in their solar thermal energy storage and temperature-regulated property, but also make the colored latex paint coating have superb colored fixing capabilities.     

Preparation,Mechanical and Thermal Properties of Cement Board with Expanded Perlite Based Composite Phase Change Material for Improving Buildings Thermal Behavior

Here we demonstrate the mechanical properties, thermal conductivity, and thermal energy storage performance of construction elements made of cement and form-stable PCM-Rubitherm^® RT 28 HC (RT28)/expanded perlite (EP) composite phase change materials (PCMs). The composite PCMs were prepared by adsorbing RT28 into the pores of EP, in which the mass fraction of RT28 should be limited to be no more than 40 wt %. The adsorbed RT28 is observed to be uniformly confined into the pores of EP. The phase change temperatures of the RT28/EP composite PCMs are very close to that of the pure RT28. The apparent density and compression strength of the composite cubes increase linearly with the mass fraction of RT28. Compared with the thermal conductivity of the boards composed of cement and EP, the thermal conductivities of the composite boards containing RT28 increase by 15%–35% with the mass fraction increasing of RT28. The cubic test rooms that consist of six boards were built to evaluate the thermal energy storage performance, it is found that the maximum temperature different between the outside surface of the top board with the indoor temperature using the composite boards is 13.3 °C higher than that of the boards containing no RT28. The thermal mass increase of the built environment due to the application of composite boards can contribute to improving the indoor thermal comfort and reducing the energy consumption in the buildings.     

Phase Change Materials Composite Based on Hybrid Aerogel with Anisotropic Microstructure

Phase change materials (PCMs) can be thermally enhanced by reduced graphene oxide (rGO)/expanded graphite (EG) aerogel with anisotropic microstructure. An rGO/EG aerogel with anisotropic microstructure was prepared by directionally freezing aqueous suspensions of graphene oxide (GO) and EG, followed by a freeze-drying process and thermal reduction at 250 °C. The anisotropic microstructure of rGO/EG aerogel composite PCM was confirmed by scanning electron microscopy (SEM), thermal conductivity tests and infrared images. The thermal conductivity of PCMs increased remarkably with rGO/EG aerogel. Compared with the thermal conductivity of pure paraffin, it increased by about 50~300% in the longitudinal direction and increased by about 25–150% in the transversal direction. The enhancement of thermal conductivity was attributed to the improvement of the thermal pathway provided by rGO/EG aerogel and the decrease of the interfacial thermal resistance between PCM and fillers. Meanwhile, rGO/EG aerogel was combined with paraffin only by physical adsorption, and no chemical interaction occurs between them, leading to no effect on the phase change behavior. In addition, the addition of rGO/EG aerogel led to a slight increase in the latent heat of the paraffin in the composite PCM.     

Physical Properties of an Eco-Sustainable,Form-Stable Phase Change Material Included in Aerial-Lime-Based Mortar Intended for Different Climates

The aim of this experimental investigation was to produce a form-stable phase change material (PCM) able to reduce the need for nonrenewable energy resources required for the heating/cooling of buildings located in regions characterized by different climatic conditions. The innovative PCM must also be sustainable and must be produced according to the principles of the circular economy. To achieve such ambitious goals, a form-stable, sustainable PCM was produced through vacuum impregnation. The form-stable PCM was produced starting from a low-toxicity, low-flammability polyethylene glycol of medium molecular weight (PEG 800), which was included in porous stone granules obtained as waste products of the cutting/processing of local (Lecce) stone. The thermal properties and thermal stability of PEG 800 and of its PCM-composite were evaluated by employing differential scanning calorimetry (DSC) and thermo-gravimetric analysis (TGA). The appropriate parameters to perform the impregnation procedure were identified through rheological and calorimetric analyses. A simple leakage test was performed to assess if the PEG polymer can leak from the stone flakes. Finally, the new PCM was added as an aggregate in aerial-lime-based mortars, and the mortar’s properties were analyzed in fresh (workability) and hardened (flexural and compressive strength and thermal characteristics) states for potential applications, particularly in ancient buildings.     

Novel 3D Printing Phase Change Aggregate Concrete: Mechanical and Thermal Properties Analysis

The use of phase change materials (PCMs) in concrete is a double-edged sword that improves the thermal inertia but degrades the mechanical properties of concrete. It has been an essential but unsolved issue to enhance the thermal capacity of PCMs while non-decreasing their mechanical strength. To this end, this work designs a novel 3D printing phase change aggregate to prepare concrete with prominent thermal capacity and ductility. The work investigated the effects of 3D printing phase change aggregate on the compressive strength and splitting tensile strength of concrete. The compressive strength of phase change aggregate concrete is 21.18 MPa, but the ductility of concrete improves. The splitting tensile strength was 1.45 MPa. The peak strain is 11.69 × 10⁻³, nearly 13 times that of basalt aggregate concrete. Moreover, using 3D printing phase change aggregate reduced concrete’s early peak hydration temperature by 7.1%. The thermal insulation capacity of the experiment cube model with phase change concrete has been improved. The results show that the novel 3D printing change aggregate concrete has good mechanical properties and latent heat storage, providing a guideline for applying PCMs in building materials.     

Preparation and Characterization of Paraffin/Mesoporous Silica Shape-Stabilized Phase Change Materials for Building Thermal Insulation

The use of phase change materials (PCMs) is an attractive method for energy storage and utilization in building envelopes. Here, shape-stabilized phase change materials (SS-PCMs) were prepared via direct adsorption using mesoporous silica (MS) with different pore diameters as the support matrix. The leakage properties, microstructure, chemical structure, thermophysical properties, activation energy, thermal stability and thermal storage-release characteristics of paraffin and SS-PCMs were investigated. The results show that the maximum mass proportion of paraffin in SS-PCMs is 70% when the average pore diameter of mesoporous silica is 15 nm, and the phase change temperature and latent heat of the corresponding SS-PCM are 23.6 °C and 135.4 kJ/kg, respectively. No chemical reaction occurs between mesoporous silica and paraffin and the SS-PCMs exhibit high thermal stability. The high activation energy of the paraffin (70%)/MS1 SS-PCM verifies that the shape and thermal properties can be maintained stably during phase change conversions. The time required for SS-PCMs to complete the thermal storage and release process is reduced by up to 34.0% compared with that for pure paraffin, showing a decline in the thermal conductivity of SS-PCMs after the addition of mesoporous silica. Hence, the prepared paraffin/MS SS-PCMs, in particular paraffin (70%)/MS1 SS-PCM, can be used for storing thermal energy and regulating indoor temperature in buildings.     

Preparation and Characteristics of Na2HPO4·12H2O-K2HPO4·3H2O/SiO2 Composite Phase Change Materials for Thermal Energy Storage

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.