Phase Change Materials Content Research Articles

Magnetic Phase-Change Microcapsules with High Encapsulation Efficiency, Enhancement of Infrared Stealth, and Thermal Stability

Due to energy shortages and the greenhouse effect, the efficient use of energy through phase-change materials (PCMs) is gaining increased attention. In this study, magnetic phase-change microcapsules (Mag-mc) were prepared by suspension polymerization. The shell layer of the microcapsules was formed by copolymerizing methyl methacrylate and triethoxyethylene silane, with the latter enhancing the compatibility of the shell layer with the magnetic additive. Ferric ferrous oxide modified by oleic acid (Fe3O4(m)) was added as the magnetic additive. Differential scanning calorimetry (DSC) testing revealed that the content of phase-change materials in microcapsules without and with ferric ferrous oxide were 79.77% and 96.63%, respectively, demonstrating that the addition of Fe3O4(m) improved the encapsulation efficiency and enhanced the energy storage ability of the microcapsules. Laser particle size analysis showed that the overall average particle sizes for the microcapsules without and with ferric ferrous oxide were 3.48 μm and 2.09 μm, respectively, indicating that the incorporation of magnetic materials reduced the size and distribution of the microcapsules. Thermogravimetric analysis indicated that the thermal stability of the microcapsules was enhanced by the addition of Fe3O4(m). Moreover, the infrared emissivity of the microcapsule-containing film decreased from 0.77 to 0.72 with the addition of Fe3O4(m) to the shell of microcapsules.

Thermal and mechanical performance assessment of composite (CPCM) for energy storage

Phase change materials (PCMs) face obstacles in being widely used due to issues with heat transfer and maintaining their shape. In this research, instead of using binders, the Hexadecane (H) is melted in such a way that the capillary forces of the molten wax allow it to be impregnated into the low-density polyethylene (P) molecules and bind it together as a composite. It was found that the hot melt extrusion (HME) combines the two materials at the micro-scale, forming a phase change composite (CPCM) with various geometries that possesses superior latent heat and shape stability during phase transition. The structure can incorporate a higher percentage of PCM (60 %) using this method, which also results in lower costs. According to the thermal analysis, (H60P40) provides great thermal stability and can store a lot of energy per unit of weight. It has a high capacity of storing latent heat at 129.56 J/g and can also prevent Hexadecane leakage. Based on the mechanical properties results, hexadecane acts like plasticizer thus the addition of PCM decreases Young's modulus, stress in break, and stress at yield. This trend is observed as the PCM content increases. The high values of elongation at break also indicates the strong plasticizing properties of PCM. Based on the obtained results, the CPCMs as a potential candidate for an application in buildings for thermal regulation, reducing energy consumption, and reducing indoor temperature swing.

A shape-stable phase change material for high-temperature thermal energy storage based on coal fly ash and Na2SO4-K2SO4

Using coal fly ash (CFA) as the skeleton material and binary sulfates of Na2SO4-K2SO4 as the phase change material (PCM), high-temperature coal fly ash based phase change thermal storage materials (CPCM) were successfully synthesized. The influences of CFA fractions and types on the morphology, physicochemical properties, and thermal characteristics of the composites were intensively investigated. Results show that the heat storage density and thermal conductivity of CPCMs increase with the PCM content. Particularly, the CPCM60-A composite, comprising 60 wt% Na2SO4-K2SO4 eutectic and 40 wt% CFA-A, exhibits excellent chemical compatibility and stable shape retention after sintering. Furthermore, CPCM60-A demonstrates the highest phase change latent heat of 60.43 J/g and thermal conductivity of 0.61 W/(m·K). The influence of CFA types reveals that CFA-A with a higher ratio of SiO2 and Al2O3, lower carbon content, and a rich porous structure is more suitable to fabricate molten salt heat storage materials. This work demonstrates that CFA, a byproduct of coal-fired industry, is a promising skeleton material for the fabrication of high-temperature CPCM composites, offering a novel approach for enhancing the efficiency and cost-competitiveness of solar power and waste heat recovery systems.

Thermally Active Medium-Density Fiberboard (MDF) with the Addition of Phase Change Materials for Furniture and Interior Design.

No matter where we reside, the issue of greenhouse gas emissions impacts us all. Their influence has a disastrous effect on the earth's climate, producing global warming and many other irreversible environmental impacts, even though it is occasionally invisible to the independent eye. Phase change materials (PCMs) can store and release heat when it is abundant during the day (e.g., from solar radiation), for use at night, or on chilly days when buildings need to be heated. As a consequence, buildings use less energy to heat and cool, which lowers greenhouse gas emissions. Consequently, research on thermally active medium-density fiberboard (MDF) with PCMs is presented in this work. MDF is useful for interior design and furniture manufacturing. The boards were created using pine (Pinus sylvestris L.) and spruce (Picea abies L.) fibers, urea-formaldehyde resin, and PCM powder, with a phase transition temperature of 22 °C, a density of 785 kg m-3, a latent heat capacity of 160 kJ kg-1, a volumetric heat capacity of 126 MJ m-3, a specific heat capacity of 2.2 kJ kgK-1, a thermal conductivity of 0.18 W mK-1, and a maximum operating temperature of 200 °C. Before resination, the wood fibers were divided into two outer layers (16%) and an interior layer (68% by weight). Throughout the resination process, the PCM particles were solely integrated into the inner layer fibers. The mats were created by hand. A hydraulic press (AKE, Mariannelund, Sweden) was used to press the boards, and its operating parameters were 180 °C, 20 s/mm of nominal thickness, and 2.5 MPa for the maximum unit pressing pressure. Five variants of MDF with a PCM additive were developed: 0%, 5%, 10%, 30%, and 50%. According to the study, scores at the MOR, MOE, IB, and screw withdrawal resistance (SWR) tests decreased when PCM content was added, for example, MOE from 3176 to 1057 N mm-2, MOR from 41.2 to 11.5 N mm-2, and IB from 0.78 to 0.27 N mm-2. However, the results of the thickness swelling and water absorption tests indicate that the PCM particles do not exhibit a substantial capacity to absorb water, retaining the dimensional stability of the MDF boards. The thickness swelling positively decreased with the PCM content increase from 15.1 to 7.38% after 24 h of soaking. The panel's thermal characteristics improved with the increasing PCM concentration, according to the data. The density profiles of all the variations under consideration had a somewhat U-shaped appearance; however, the version with a 50% PCM content had a flatter form and no obvious layer compaction on the panel surface. Therefore, certain mechanical and physical characteristics of the manufactured panels can be enhanced by a well-chosen PCM addition.

Thermal Energy Storage in Concrete by Encapsulation of a Nano-Additivated Phase Change Material in Lightweight Aggregates.

This work discusses the applicability of lightweight aggregate-encapsulated n-octadecane with 1.0 wt.% of Cu nanoparticles, for enhanced thermal comfort in buildings by providing thermal energy storage functionality to no-fines concrete. A straightforward two-step procedure (impregnation and occlusion) for the encapsulation of the nano-additivated phase change material in lightweight aggregates is presented. Encapsulation efficiencies of 30-40% are achieved. Phase change behavior is consistent across cycles. Cu nanoparticles provide nucleation points for phase change and increase the rate of progression of phase change fronts due to the enhancement in the effective thermal conductivity of n-octadecane. The effective thermal conductivity of the composites remains like that of regular lightweight aggregates and can still fulfil thermal insulation requirements. The thermal response of no-fines concrete blocks prepared with these new aggregates is also studied. Under artificial sunlight, with a standard 1000 W·m-2 irradiance and AM1.5G filter, concrete samples with the epoxy-coated aggregate-encapsulated n-octadecane-based dispersion of Cu nanoparticles (with a phase change material content below 8% of the total concrete mass) can effectively maintain a significant 5 °C difference between irradiated and non-irradiated sides of the block for ca. 30 min.

Study on phase change materials integration in concrete: Form-stable PCM and direct addition

As the economy continues to develop, building energy consumption rises, necessitating sustainable solutions. Concrete, a pivotal building material, assumes a vital role in this context. To address the challenge of escalating energy consumption and environmental impact, this study studied the integration of phase change materials (PCMs) into concrete by two methods. Recycled aggregates serve as form-stable mediums for PCM absorption, while direct addition methods incorporate 7.5 % and 15 % free liquid PCM by volume of river sand. Six concrete mixtures underwent comprehensive evaluation encompassing workability, density, water absorption by immersion, compressive strength, flexural strength, chloride ion penetration, freeze-thaw cycling tests, and carbonation. The results reveal a decrease in concrete density and mechanical properties with increasing PCM content. Nevertheless, notable enhancements in chloride ion penetration resistance, reaching up to 18.5 % with free PCM incorporation, and zero carbonation depth were observed. These results underscore the potential of PCM-concrete composites in harmonizing energy efficiency and structural integrity, offering a sustainable alternative to fossil fuel-based air conditioning systems and with great potential from the point of view of the durability of the structures.

Microencapsulation of phase change materials (PCMs) at low temperature using a novel thin film UV reactor

Phase-change materials (PCMs) have shown great promise for energy management in buildings and gained attention in the field of sustainable and energy-efficient construction. However, to fully utilize PCMs, their proper containment is vital. In this study, a photo-induced polymerization process using a new thin film UV reactor at room temperature for PCM microencapsulation in polymer shells of different acrylate-based monomers was investigated. Four different acrylate-based monomers were investigated: namely, methyl methacrylate (MMA), ethyl acrylate (EAA), butyl acrylate (BAA), and tert-butyl acrylate (TBMA). Commercial Rubitherm’s RT21 PCM (Tpeak,melting ∼ 21 °C and ΔH = 123 kJ/kg) and Irgacure® 819 as a photosensitive initiator were used. When MMA or EAA were used, scanning electron microscopy (SEM) images revealed smooth surfaces of PCM microcapsules (m-PCMs) with a hemispherical shape. While m-PCMs with rough surfaces, buckles, and dimples were found when BAA and TBMA were applied. The results showed that the highest levels of microencapsulation efficiency, yield, and PCM content were observed for MMA and EAA samples. The TBMA sample shows low values of microencapsulation efficiency and yield (about 29.1 and 53.4 %, respectively). Furthermore, results showed that adding cross-linking agents to the recipe has had multiple favourable effects. It has mitigated sub-cooling, increased PCM content, improved microencapsulation efficiency, and boosted the overall yield of PCM. In conclusion, the current work will contribute to the development of a microencapsulation technology of PCMs that overcomes the shortcomings of long time and high temperature needed in the present traditional microencapsulation procedure.

Performance evaluation and optimization of compact tube-fin latent heat storage system in phase change nanoemulsion discharge mode

The low thermal conductivity of phase change materials (PCMs) and the reduced heat transfer temperature difference along a tube both limit the thermal performance of latent heat thermal energy storage (LHTES). Herein, a compact tube-fin LHTES system based on phase change nanoemulsions was developed and the heat transfer process of nanoemulsion and PCM was numerically investigated. The effects of the heat transfer structure of the heat exchanger and the thermophysical parameters of the heat transfer fluid (HTF) on the cold energy discharge performance of the system were quantified. The optimized model reduced the discharge time by 24.4 % in nanoemulsion mode relative to water. Heat transfer improvement on the PCM side could be achieved by decreasing the fin spacing and tube spacing and by increasing the fin thickness. Such improvement reinforced the heat transfer enhancement of the nanoemulsion. The heat transfer mechanism was explained by the temperature distributions of the HTF and PCM along the tube. The phase-change thermostatic properties of the nanoemulsion and PCM contributed to the formation of dual-phase-change coupled heat transfer (i.e., the heat transfer process when the fluid inside the tube and the PCM filled outside the tube undergo a simultaneous phase change) within the LHTES, increasing the heat transfer temperature difference and the magnitude of the driving force. Increasing the phase change temperature difference accelerated the onset of dual-phase-change heat transfer, while increasing the PCM content prolonged the process. Briefly, this study provided operational and design assistance for LHTES systems in nanoemulsion mode with the intention to accelerate heat transfer rates.

Performance analysis of solar thermal storage systems with packed bed utilizing form-stable phase change materials and heat pump integration

Solar energy, a pivotal renewable resource, faces operational challenges due to its intermittent and unstable power output. Thermal energy storage systems emerge as a promising solution, with phase change materials (PCMs) packed beds attracting attention for their compactness and stable temperature transitions. This paper details a laboratory-scale solar thermal storage PCM packed bed integrated with a heat pump, utilizing a novel form-stable PCM. A numerical model was established to assess the thermal storage characteristics and heat extraction performance of the solar PCM packed bed coupled with a heat pump. Simulation results show that increasing solar irradiance significantly reduces storage duration, achieving full thermal storage in 3.4 h at 900 W/m2 irradiance. Optimal starting times were identified as 9:00 a.m. or 11:00 a.m., with later starts resulting in incomplete storage due to the PCM not reaching its phase change temperature. Additionally, packed bed parameters influenced storage conditions; increasing the paraffin content in the PCM extended the phase change duration, while graphene nanoparticles slightly reduced it. Lower porosity (0.49) beds, with higher PCM content, reached 70 °C quicker than higher porosity (0.61) beds due to higher pressure drops promoting more uniform flow and temperature distribution. During heat extraction, coupling the heat pump at 2 liters/min achieved temperatures below 45 °C in 4.1 h, while at 6 liters/min, the time reduced to 1.6 h, demonstrating adaptability to different extraction rates. These findings provide insight into the thermal performance of solar PCM packed beds coupled with heat pumps, contributing to efficient and stable thermal utilization of solar energy.

A comprehensive experimental characterization of cement mortar containing sodium sulfate dehydrate/calcium chloride hexahydrate/graphite shape-stable PCM for enhanced thermal regulation in buildings

The current research on integrating phase change materials (PCMs) into building envelopes is driven by the need to optimize thermal performance while preserving material properties. Integrating PCM into cement mortar faces challenges in balancing heat storage capacity and material strength. Using higher PCM content may compromise strength, but smaller content may limit heat storage capacity. To overcome these hurdles, integrating high-conductive SSPCM at lower percentages can enhance thermal performance without compromising material integrity. Yet, research in this domain is lacking. This study investigates integrating a shape-stable PCM into plaster to ascertain the ideal PCM content while maintaining vital characteristics. Experimental analysis of five composites, with PCM percentages ranging from 3% to 10%, showed that all met physical property criteria except the 10% PCM composite. Despite a slight decrease in mechanical strength, it remained within acceptable standards for mortar materials. The composites exhibited improved thermal conductivity, specific heat capacity, thermal diffusivity, and heat storage capacity significantly with increasing PCM content. This study convincingly demonstrates the feasibility of maintaining thermal effectiveness even with low PCM content, offering crucial insights for developing energy-efficient building designs and promoting sustainable practices in the construction industry.

Re-Designing Cellulosic Core-Shell Composite Fibers for Advanced Photothermal and Thermal-Regulating Performance.

Flexible fibers and textiles featuring photothermal conversion and storage capacities are ideal platforms for solar-energy utilization and wearable thermal management. Other than using fossil-fuel-based synthetic fibers, re-designing natural fibers with nanotechnology is a sustainable but challenging option. Herein, advanced core-shell structure fibers based on plant-based nanocelluloses are obtained using a facile co-axial wet-spinning process, which has superior photothermal and thermal-regulating performances. Besides serving as the continuous matrix, nanocelluloses also have two other important roles: dispersing agent when exfoliating molybdenum disulfide (MoS2), and stabilizer for phase change materials (PCM) in the form of Pickering emulsion. Consequently, the shell layer contains well-oriented nanocelluloses and MoS2, and the core layer contains a high content of PCM in a leak-proof encapsulated manner. Such a hierarchical cellulosic supportive structure leads to high mechanical strength (139MPa), favorable flexibility, and large latent heat (92.0Jg-1), surpassing most previous studies. Furthermore, the corresponding woven cloth demonstrates satisfactory thermal-regulating performance, high solar-thermal conversion and storage efficiency (78.4-84.3%), and excellent long-term performance. In all, this work paves a new way to build advanced structures by assembling nanoparticles and polymers for functional composite fibers in advanced solar-energy-related applications.

Effect of blending of medium-temperature phase change material on the bitumen storage heat

This study aims to investigate the feasibility of using D-Mannitol as a phase-change material (PCM) to increase the energy storage capacity and improve the thermomechanical characteristics of the modified bitumen. D-mannitol (Dm) was incorporated into Bitumen (Bm) using a high-speed shearing method. The results showed that the integration of PCM enhanced the physical characteristics of the basic bitumen, with the modified bitumen having a melting point close to that of D-mannitol (Tm = 164 °C). The D-mannitol was found to crystallize during cooling, indicating that it can store or release heat in the latent form. The specific heat capacity of the modified bitumen was proven to increase gradually as the PCM content (2, 4, and 8 wt%) increased. The maximum temperature regulation effect of the modified bitumen was observed when the PCM content reached 8 wt%, resulting in a temperature reduction of up to 9 °C. This study provides a basis for the utilization of D-Mannitol as a form of energy storage in bitumen-based pavement applications.

Study on the Performance of Phase-Change Self-Regulating Permeable Asphalt Pavement

Under low-temperature conditions in winter, asphalt pavement is prone to cracking, icing and other distresses, which affect its safety and comfort. Therefore, by incorporating phase-change materials into asphalt and conducting relevant performance studies, the aim is to alleviate low-temperature distress and regulate road surface temperature and expand the application of phase-change materials in asphalt pavement. We mixed the selected phase-change materials with different dosages into the matrix asphalt to prepare phase-change temperature-regulating asphalt and tested the four basic indicators: road performance, latent heat characteristics, temperature-regulating performance, and rheological properties of phase-change asphalt and its mixture. The research results indicate that with the increase in phase-change material content, the penetration, softening point, ductility, and dynamic viscosity of phase-change high-viscosity asphalt gradually increase. Under the constant temperature test conditions of −2.5 °C and −5 °C, the surface icing speed of asphalt binder specimens mixed with phase-change materials is slower than that of specimens without phase-change materials. Adding phase-change materials can improve the high-temperature and low-temperature PG grading of high-viscosity asphalt, effectively improving its high-temperature rutting resistance and low-temperature cracking performance. According to the temperature regulation test results, phase-change temperature-regulating asphalt has a certain regulating effect on temperature under low-temperature conditions, which can slow down the cooling rate of asphalt, reduce the thermal conductivity of permeable asphalt mixture by more than 50%, increase the temperature regulation rate by more than 30%, and improve the ice-melting and snow-melting ability by more than 20%. Phase-change materials have almost no effect on the porosity of permeable asphalt mixtures and can effectively improve the water stability, low-temperature crack resistance, and antiflying performance of permeable asphalt mixtures. Their Marshall stability and rutting stability decrease, but still meet the requirements of the specifications. Applying phase-change materials to permeable asphalt pavement can automatically adjust the temperature of the pavement, reduce the cooling rate of the asphalt pavement during cooling, alleviate the problem of snow and ice accumulation on the asphalt pavement in winter, and thereby improve the performance of permeable asphalt pavement against freeze–thaw cycles.

The impact of different fin configurations and design parameters on the performance of a finned PCM heat sink

This work builds on our recent research on finned phase change material (PCM) heat sinks, where we proposed a novel Gallium based PCM heat sink concept that counter-intuitively incorporated fins detached from the hot sink base instead of being fully attached to it. The detached and fully attached fin configurations studied utilized the same overall fin size and material resources. The attached fin approach offered less outer fin surface area exposed to the ambient surroundings and less PCM capacity compared with the detached fin approach. However, the attached fin approach facilitated a more direct path for the heat dissipation into the ambient surroundings via the fin body. As an extension of the previous work, the present work explores finned heat sinks that combine the advantages of the above two approaches. First, we present results for two limiting baseline cases of the two finning categories: attached fins with lower outer fin surface area and less PCM and detached fins with a larger exposed fin area and more PCM. Next, we study a heat sink case with attached fins tall enough to have a total outer fin surface area equivalent to the outer surface area of the detached fins case but with less PCM content. Subsequently, we consider cases of fully attached fins with the same total outer fin area and the same total PCM capacity as the detached fins baseline case. Here, we achieve the same PCM content in the sink while still having fully attached fins simply by increasing the overall heat sink size to accommodate additional PCM. This is done in two ways: (1) by expanding the heat sink size in the horizontal direction (i.e., increasing the heat sink width) at constant heat sink height, and (2) by expanding the heat sink height at constant heat sink width. In this work, we propose the best way to utilize the resources in terms of used PCM and used fin content in the heat sink space to achieve the ultimate goal of attaining lowest peak temperatures.

Improving thermal storage of energy screw pile groups with phase change materials

To achieve affordable housing in a carbon-neutral society, new buildings require a dual-purpose approach that comprises efficient construction and a green energy supply. Energy screw piles [1, 7] meet this demand as they combine the agility of screw pile drilling with the capability of extracting clean shallow geothermal energy. Moreover, the screw piles can be filled with phase change materials (PCM) to provide latent thermal storage. Studies regarding the use of PCMs as borehole backfill in a ground source heat pump system (GSHP) conclude that PCM implementation can improve GSHP performance. However, most commercially available PCMs have low thermal conductivities (λ) which undermine heat exchange rates [5, 10]. Besides, using PCMs as a composition of a concrete energy pile can reduce the pile structural performance since PCMs usually have a low mechanical capacity [2, 8]. The authors recently introduced PCM-sand mixtures as a core in the central hollow part of an energy screw pile, which does not impact the pile structural capacity [6]. The mixtures with a higher PCM content benefit the pile heat exchange through its latent heat, but only when the PCM does not reduce the mixture’s λ. To overcome this problem, this work tests a new underground heat exchange system where instead of mixing the PCM in the energy screw pile filling material, regular screw piles (i.e., without the heat exchange tubes) are filled with pure PCM, acting as thermal storage piles. A numerical model built via COMSOL [4] is used to evaluate how this combination of screw piles performs thermally when supplying/rejecting heat for a GSHP system operating for a whole year.
 This work uses a validated numerical model [3, 9] to simulate a grid of evenly distributed screw piles, where Energy Piles (EP) and Thermal Storage Piles (TSP) are positioned interspersed, evenly spaced 0.7 m apart. Inside the EPs, an U-loop pipe is inserted in the pile steel case and the remaining is filled with grout. In contrast, the steel case of the TSPs is filled with only PCM [11]. All other material properties and the screw pile geometry are based on [1]. The thermal load is based on the design of a building located in Melbourne, Australia (Figure 1(a)). The model considers the hourly operation of a GSHP for one year, calculating the GSHP Coefficient of performance (COP) at every time step and adjusting the ground thermal load. For comparison, two simulations (one where the TSPs are filled with PCM and a reference where they are filled with only air) are undertaken. Besides the energy stored, the COPs of both cases are compared as a relative increase/decrease percentage (COPchange = (COPPCM / COPReference) – 1).
 Figure 1(b) presents the energy stored by the PCM and its corresponding percentage in a solid state over the simulation. As the EPs reject heat underground due to GSHP summer operation for cooling, the TSPs temperature rise and store sensible heat, until they reach their phase change temperature (Tpc), when the PCM melts to store significantly more heat energy in a shorter time window due to latent heat. Conversely, the PCM solidifies when EPs extract more heat than reject due to GSHP winter operation (heating) for a certain period. The PCM melts again on the following summer, restarting the whole process. The peak energy stored in the TSPs is 190.3 MJ/m3. Even though the thermal load varies hourly, the PCM phase change process happens without immediate responses to the load variation. Figure 1(c) presents the resulting change in the hourly COP considering cooling (CCOP) and heating (HCOP) from implementing PCM in the TSPs, compared to the reference scenario (empty TSPs). The extra heat stored by the PCM lowers the circulating fluid temperature while the latent heat is engaged (months 2 to 7 and 12), which results in a higher CCOP and a lower HCOP. By plotting a monthly average of the COPchange (grey markers), it is clear that the impact of the PCM on the COP is positive when cooling is dominant and slightly negative when heating becomes dominant while the latent heat is engaged. When the PCM is implemented in the EP [6, 10], the heat exchanged by the EP drops once the phase change process is over due to the low λ of the PCM, but by positioning it outside the EP the higher CCOP is sustained even after the phase change ends. However, lowering the fluid temperature increases CCOP while lowering HCOP at the same time, which can harm thermal performance if not designed properly. The results underlie the thermal storage potential available not only in screw piles, but also in any hollow pile foundation, by simply implementing PCM in the hollow case.

Biomass-Based Shape-Stabilized Composite Phase-Change Materials with High Solar-Thermal Conversion Efficiency for Thermal Energy Storage.

To alleviate the increasing energy crisis and achieve energy saving and consumption reduction in building materials, preparing shape-stabilized phase-change materials using bio-porous carbon materials from renewable organic waste to building envelope materials is an effective strategy. In this work, pine cone porous biomass carbon (PCC) was prepared via a chemical activation method using renewable biomaterial pine cone as a precursor and potassium hydroxide (KOH) as an activator. Polyethylene glycol (PEG) and octadecane (OD) were loaded into PCC using the vacuum impregnation method to prepare polyethylene glycol/pine cone porous biomass carbon (PEG/PCC) and octadecane/pine cone porous biomass carbon (OD/PCC) shape-stabilized phase-change materials. PCCs with a high specific surface area and pore volume were obtained by adjusting the calcination temperature and amount of KOH, which was shown as a caterpillar-like and block morphology. The shape-stabilized PEG/PCC and OD/PCC composites showed high phase-change enthalpies of 144.3 J/g and 162.3 J/g, and the solar-thermal energy conversion efficiencies of the PEG/PCC and OD/PCC reached 79.9% and 84.8%, respectively. The effects of the contents of PEG/PCC and OD/PCC on the temperature-controlling capability of rigid polyurethane foam composites were further investigated. The results showed that the temperature-regulating and temperature-controlling capabilities of the energy-storing rigid polyurethane foam composites were gradually enhanced with an increase in the phase-change material content, and there was a significant thermostatic plateau in energy absorption at 25 °C and energy release at 10 °C, which decreased the energy consumption.

Impact of gypsum mortars functionalized with phase change materials in buildings

The construction industry needs to adopt raw materials with less environmental impact and functional raw materials. The utilization of phase change materials (PCM) in interior mortars allows the energy efficiency of buildings improvement, based on solar energy, a renewable and clean energy source. On the other hand, the selection of mortars based in binders whose production emits lower carbon dioxide emissions than cement, like gypsum, can be a promising solution in help to minimize carbon dioxide (CO2) emissions and the energy consumption for raw materials production. The main objective of this work was the development and characterization of gypsum-based mortars functionalized with PCM. Four distinct mortars were developed with different contents of pure and non-encapsulated PCM (0 %, 5 %, 10 % and 20 %). The different mortars were tested from a physical and mechanical point of view. The thermal performance of the mortars according to the summer and spring seasons of the north part of Portugal and an economic analysis of the application of these mortars in a typical Portuguese building were also carried out.The results obtained allow to observe that the incorporation of 20 % PCM leads to a decrease in the water absorption by capillarity, water absorption by immersion, flexural and compressive strengths of about 65 %, 30 %, 47 % and 59 %, respectively. However, its applicability has not been compromised. The thermal performance of the PCM mortars was improved, based in the temperature range and heating and cooling needs decrease. Regarding to the summer season it was observed a maximum temperature decrease of 2.3 °C, a minimum temperature increase of 2.6 °C and a decrease of cooling and heating needs of 13 % and 21 %, respectively. Concerning to the spring season it was verified a maximum temperature decrease of 2.7 °C, a minimum temperature increase of 1.9 °C and a decrease of cooling and heating needs of 100 % and 16 %, respectively. The cost analysis revealed savings in electricity costs for buildings climatization of around 17 % during the summer season and around 59 % during the spring season.

Effects of Phase Change Materials on the Freeze–Thaw Performance of Expansive Soil

Freeze–thaw cycles can deteriorate the expansive soil performance. Phase change materials (PCMs) absorb and store heavy latent heat from the environment, which can be utilized to mitigate freeze–thaw deteriorations in expansive soil. In this study, an environmentally friendly paraffin-based PCM was selected, which included two different forms: liquid (pPCM) and microcapsules (mPCM). The volume change, mechanical properties, thermal properties, and microstructure of the improved soil were studied. These results showed that PCMs can release considerable thermal energy during phase transitions, which improves the thermal stability of the soil. The pPCM enhanced the plasticity of soil and prevented brittle failure; mPCM reduced the damage to the soil microstructure caused by freeze–thaw cycles. Macroscopically, it weakened the swell–shrink behavior and limited the degradation of the resilient modulus, unconfined compressive strength, and failure strain of expansive soil. The optimal PCM content was determined based on the mechanical and thermal properties of the improved soil. This study provides a new idea for the engineering treatment of expansive soil in cold regions.

Numerical simulation of the anti-freezing performance of a phase change clay core-wall with loose covering

Clay core-wall of rockfill dam may endure short-term freezing or freeze–thaw cycles owing to negative temperature conditions during winter construction in cold regions, resulting in the degradation of the clay compaction, frost swelling, and cracking performance. The most commonly used insulation cover measures interfere with the continuous construction of clay core-walls, which may shorten the effective time available for construction and delay the dam construction progress. To address this problem, we proposed using the upper layer of the loose-covering clay and the latent heat of phase change materials (PCMs) to control the core-wall temperature. We implemented a numerical model for simulating the anti-freezing performance of the PCM mixed clay (PCM-clay) with loose covering. First, a heat transfer model was established using the finite element software COMSOL, and the effectiveness of the model was verified by comparing it with indoor temperature control test results. Subsequently, numerical models including different construction conditions were established, and the temperature control effect was analyzed under different loose-covering thicknesses, initial soil temperatures, and PCM contents. The results showed that at the design ambient temperature and a 2% PCM content, an effective construction time availability of two consecutive days was maintained under a 20-cm-thick loose covering. In contrast, under the same temperature conditions, but for a 4% PCM content, the effective construction time available under a 5-cm-thick loose covering was 43.1 h. Thus, the use of PCM-clay combined with the upper layer loose covering for temperature control proved feasible and effective. Additionally, by increasing the thickness of the loose covering and the initial temperature of the PCM-clay, the PCM content can be reduced. This provides a theoretical basis and a potential technical solution to maximize the time available for construction and accelerate the construction progress of core-wall rockfill dams.

Shape memory behavior of novel Ethylene Propylene Diene Monomer (EPDM)/paraffin foams

Ethylene Propylene Diene Monomer (EPDM) rubber foams are widely employed for thermal and acoustic insulation in building construction. However, their installation in confined spaces is often complicated, and the capability of EPDM foams to exhibit shape memory behavior could be a desirable property. In the literature, several works have demonstrated that blending elastomeric matrices with paraffin, a well-known Phase Change Material (PCM), could be an interesting method to obtain shape memory polymers with a tunable switching temperature. In this work, EPDM foams filled with paraffin wax, having a melting temperature of 70°C, were produced and characterized from a microstructural and thermo-mechanical point of view. By melt compounding and hot pressing, samples were produced, and the PCM content in the foams was varied between 0 and 60 wt% (with respect to the EPDM matrix). The results of the shape memory tests evidenced the crucial role played by the PCM in providing excellent shape fixability for the expanded rubber. Even a limited amount of paraffin (i.e., 20 wt%) was able to raise the strain fixity parameter to a value higher than 80%, and it reached 100% when the paraffin content was increased to 60 wt%. On the other hand, an increased PCM fraction caused a slower recovery process. Consequently, a compromise between a fast recovery and optimum shape fixability should be accepted. These results are promising for the development of novel thermal and acoustic EPDM insulating foams easier to be installed.