Thermal Regulation Performance Research Articles

Novel thermal-regulation and temperature-responsive controlled-release fibermats with porous sheath-core structures

Active regulation of the wound microenvironment as well as on-demand drug delivery have proven to be effective ways to accelerate wound healing, and the development of advanced textiles offers feasibility. A novel fibermat with thermal-regulation and temperature-responsive controlled-release properties was fabricated by using coaxial electrospinning, consisting of porous sheath-core polylactic acid (PLA)/ polyethylene glycol (PEG) fibers. The pore generation in the PLA shell of the PLA/PEG fiber was achieved through a phase separation method. The fiber diameter and pore size of the obtained fiber could be controlled by adjusting the flow rate of shell solution during electrospinning. Increasing the flow rate of shell solution form 0.8 mm·min-1 to 1.4 mm·min-1 resulted in an increase in fiber diameter from 4.8 μm to 15.3 μm, and an increase in pore size from 59.4 nm to 305.6 nm. Due to the high enthalpy and coverage of the PEG core, the PLA/PEG fibermats exhibited excellent thermal-regulation performance, with a surface temperature that was 2.5 °C- 5.6 °C lower than that of pure PLA fibermat during heating process. On-demand release was achieved by directly controlling the core layer of the coaxial PLA/PEG fiber through temperature. The hydrophobicity of the PLA shell initially reduced burst release, followed by increased release as the temperature reached the phase transition temperature of PEG. Furthermore, this advanced fibermat demonstrated desirable moisture permeability, appropriate mechanical properties and good thermal stability, indicating broad potential applications in medical and health fields.

Recent Progress of Phase Change Materials and Their Applications in Facility Agriculture and Related-Buildings—A Review

Facility agriculture, which involves agricultural production in controlled environments such as greenhouses, indoor farms, and vertical farms, aims to maximize efficiency, yield, and quality while minimizing resource consumption and environmental impact. Energy-saving technologies are essential to the green and low-carbon development of facility agriculture. Recently, phase change heat storage (PCHS) systems using phase change materials (PCMs) have gained significant attention due to their high thermal storage density and excellent thermal regulation performance. These systems are particularly promising for applications in facility agriculture and related buildings, such as solar thermal utilization, greenhouse walls, and soil insulation. However, the low thermal conductivity of PCMs presents a challenge for applications requiring rapid heat transfer. This study aims to provide a comprehensive review of the types, thermophysical properties, and various forms of PCMs, including macro-encapsulated PCMs, shape-stabilized PCMs, and phase change capsules (PCCs), as well as their preparation methods. The research methodology involves an in-depth analysis of these PCMs and their applications in active and passive PCHS systems within facility agriculture and related buildings. The major conclusion of this study highlights the critical role of PCMs in advancing energy-saving technologies in facility agriculture. By enhancing PCM performance, optimizing latent heat storage systems, and integrating intelligent environmental control, this work provides essential guidelines for designing more efficient and sustainable agricultural structures. The article will serve as the fundamental guideline to design more robust structures for facility agriculture and related buildings.

The effect of feeding rate ratio on the properties of coaxial electrospun PLA/PEG nanofibers

AbstractIn order to clarify the effect of feeding rate ratio (Rsr) for polylactic acid (PLA) to polyethylene glycol (PEG) on the performance of thermal regulation nanofibers, PLA and PEG solutions were used as the outer and inner spinning solutions, respectively, to develop PLA/PEG nanofibers (NFp‐p) through coaxial electrospinning. NFp‐p nanofibers with Rsr of 2:1, 3:1, and 4:1 were labeled PR1, PR2, and PR3, respectively. The morphology, chemical structure, mechanical properties, and thermal performance of NFp‐p were tested, and the thermal regulation function was investigated. The results showed that increasing Rsr could increase the diameter of NFp‐p, with PR1 having the smallest average diameter (520 nm). PR1 had the lowest water contact angle (122.4°), and higher Rsr enhanced the encapsulation effect of PLA on PEG. The mechanical properties of NFp‐p were significantly improved compared to pure PLA, with PR1 and PR3 exhibiting the highest breaking stress (2.5 MPa) and breaking strain (213%). The thermal performance of NFp‐p could be regulated by Rsr, with PR1 showing a more pronounced endothermic peak due to the melting of PEG, and the highest phase‐change enthalpy (13.2 J/g). Lower Rsr enhanced the thermal regulation function of NFp‐p, and PR1 showed superior thermal regulation performance.

Microfluidic fabrication of compound microfibers encapsulating nano-enhanced phase change material (PCM) for thermal regulation

This study presents a microfluidic approach for fabrication of compound phase change fibers (CPCFs) encapsulating nano-enhanced phase change material (PCM), RT25, for thermal regulation. The produced fibers are flexible and have strong compatibility and durable stability, with their size and the proportion of PCM can be precisely controlled by the microfluidic approach. Especially, a hydroxy surface modification method was used to uniformly disperse SiO2 nanoparticles into the RT25, aiming to enhance the thermal regulation performance of the CPCFs. Thermal performance test was conducted and it indicated that, compared with the compound phase change fiber (CPCF) with pure RT25, the CPCF incorporated with 2 wt% SiO2 nanoparticles presented a notable increase in thermal conductivity by 46.52 % and 45.51 % for solid-state and liquid-state enclosed PCM with a limited reduction in both melting and solidification enthalpies by 9.21 % and 10.1 %, respectively. Moreover, an experiment simulating the heat dissipation scenario of the electronic cabinet under intermittent running with short operation and long rest was conducted by using the CPCFs. It showed that adding SiO2 nanoparticles can improve the heat absorption process (solid-to-liquid phase) via the CPCFs with a smaller temperature increase (i.e., the maximum temperature of simulated inner electronic device in the cabinet for the repeated intermittent running) and it is also able to make the CPCFs renew (liquid-to-solid phase) more quickly and ready for heat absorption process in the next cycle. These CPCFs offer a promising alternative for more efficient and sustainable thermal management of the electrical/electronic equipment.

Model-based control strategy with linear parameter-varying state-space model for rack-based cooling data centers

Cooling system energy consumption occupies approximately 40% of the total energy consumption in data centers, and efficient control is crucial for improving cooling efficiency and reducing the operational costs of data centers. This paper introduced a novel economic model predictive control (EMPC) strategy based on a linear parameter-varying state-space model. The primary objective was to maintain the thermal environment of data centers while minimizing the energy consumption of the cooling system. Therein, a linear parameter-varying state-space model was developed based on the parameter identification method to precisely predict the temperature field of the rack-based cooling data center in real-time. The energy management and thermal regulation performance of the EMPC and the proportion integration differentiation (PID) controller were comparatively analyzed through simulation experiments. Moreover, the impacts of the server workload level and optimization time domain on the performance of EMPC were comprehensively investigated. The results show that, the proposed EMPC was able to minimize the energy consumption by optimizing the supplied cold air temperature and airflow rate simultaneously. In comparison with the PID controller, EMPC not only achieves a 9.7% energy saving by preventing server over-cooling but also diminishes server temperature fluctuations, promoting the safe and stable operation of the server. The research shows that the EMPC reveals excellent performance along with all server workload levels. In addition, the length of the prediction horizon has a notable impact and three minutes is suggested for the rack-based cooling system.

Effect of evaporator curvature on the local non-equilibrium heat regulation in two-phase closed thermosyphon embankment in permafrost regions

The evaporator curvature can affect the heat transfer performance of two-phase closed thermosyphons (TPCTs) in permafrost regions. To explore the working features and control performance of TPCTs with different evaporator curvatures, two types of TPCTs with horizontal and inclined evaporator were designed. Then, a series of scale embankment models were conducted to test the thermal and deformation performance of the two TPCTs, including a TPCT embankment with inclined evaporator, a TPCT embankment with horizontal evaporator, and a contrast embankment without TPCTs. The results show that the thermal regulation performance of the TPCT with horizontal evaporator is much better than that with inclined evaporator. The thermal regime difference caused by the vapour-liquid interface interaction occurs in the whole pipe domain above the liquid pool for the TPCT with inclined evaporator while it mainly exists in the condenser domain for the TPCT with horizontal evaporator. Meanwhile, the TPCT with horizontal evaporator can decrease the temperature gradient, and thus weaken the frost heave of the embankment. Consequently, the TPCT with horizontal evaporator is more appropriate to adjust the local non-equilibrium heat process in embankment. The findings of this study supply a scientific reference for the design of TPCTs embankment in permafrost regions.

Achieving heat storage coatings from ethylene vinyl acetate copolymers and phase change nano-capsules with excellent flame-retardant and thermal comfort performances

The heat-storage coatings from ethylene vinyl acetate (EVA) copolymers were developed by incorporating in-situ synthesized phase change nano-capsules (NEPCMs). The coatings were applied to the interior walls of the building, aimed at enhancing thermal storage and flame-retardant performances. Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) are utilized to evaluate the chemical composition of the NEPCMs. At the same time, the thermal properties and microstructure of NEPCMs and the coatings are analyzed using differential scanning calorimetry (DSC) and scanning electron microscopy (SEM). The enthalpy of NEPCMs is 158.14 J/g, while that of heat-storage coatings is 56.45 J/g. NEPCMs and heat-storage coatings exhibit excellent thermal storage performance even after 200 heating-cooling cycles, demonstrating the excellent thermal stability of NEPCMs and heat-storage coatings. Furthermore, excellent flame-retardant properties are also provided by the heat-storage coating. In dynamic heat transfer experiments, under the same conditions, the heat-storage coatings were capable of maintaining the chamber in the thermal comfort zone (24–28 °C) for 141 min, while the conventional coatings lasted only 34 min. The results show that incorporating heat-storage coatings can effectively enhance the thermal regulation performance of interior walls and improve the thermal comfort of indoor environments. Therefore, heat-storage coatings hold a high potential for application in energy-saving buildings.

Sustainable Thermal Regulation of Electronics via Mitigated Supercooling of Porous Gallium-Based Phase Change Materials.

Gallium liquid metal is one of the promising phase change materials for passive thermal management of electronics due to their high thermal conductivity and latent heat per volume. However, it suffers from severe supercooling, in which molten gallium does not return to solid due to the lack of nucleation. It may require 28.2 °C lower temperature than the original freezing point to address supercooling, leading to unstable thermal regulation performance along fluctuations of cooling condition. Here, gallium is infused into porous copper in an oxide-free environment, forming intermetallic compound impurities at the interfaces to reduce the activation energy for heterogeneous nucleation. The porous-shaped gallium provides ≈63% smaller supercooling than that of the bulk type due to large specific surface area (≈9,070 cm2 per cm3) and high wetting characteristics (≈16° of contact angle) on CuGa2 intermetallic layer. During repetitive heating-cooling cycles, porous-shaped gallium consistently shows propagation of crystallization at even near room temperature (≈25 °C) while maintaining stable performance as thermal buffer, whereas droplet-shaped gallium is gradually degraded due to partial-supercooled state. The findings will improve the responsive thermal regulation performance to relieve a rapid increase in temperature of semiconductors/batteries, and also have a potential for energy storage applications.

Novel integration of recycled-hemihydrate phosphogypsum and ethyl palmitate in composite phase change material for building thermal regulation

This study investigates the properties of novel heat storage gypsum composites composed of waste Hemihydrate phosphogypsum (HP) incorporated with Ethyl Palmitate (EP) Phase Change Material (PCM) at varying concentrations of 25 wt %, 50 wt %, and 75 wt %. The focus of the research revolves around evaluating key characteristics, including leakage properties, chemical stability, microstructural analysis, heat storage characteristics, mechanical properties, and the thermal regulation performance of these novel composites. The investigation of leakage properties aimed to find the optimum EP ratio within the composite structure without causing any potential EP leakage, and it was determined to be 25 wt %. Furthermore, thermal regulation tests are conducted to assess the heat storage and release capabilities of the composites with varying HP/EP content. The latent heat storage of the HP/EP composite was determined as 46.12 J/g, even after the 750th cycle, the value only decreased to 46.03 J/g. With the porosity filling effect of EP additive in HP, as the EP additive increased, the amount of porosity decreased, and the compressive strength values increased by almost 10 %. In hot weather conditions, the EP additive provided a cooler environment between 2 and 4 °C according to thermoregulation results. This study not only holds promise in the context of developing novel heat storage composites for applications in energy-efficient building materials, thermal energy storage systems, and related sustainable technologies but also in harnessing industrial waste byproducts. It particularly highlights the value of HP as a waste material, which has a high potential for evaluation in the production of gypsum and other building materials.

Developing Wallpaper/Dodecyl alcohol composite phase change materials as new kind of wall covering elements for building interior thermoregulation

This study introduces a novel wall-covering element consisting of wallpapers (WP) impregnated with Phase Change Material (PCM), with the aim of enhancing thermal properties and providing effective thermal regulation performance in interior spaces. The study conducts practical investigations into the thermal attributes of wallpapers (WPs) impregnated with Dodecyl alcohol (DDA) as the chosen PCM, culminating in a leakage-free WP/DDA wall covering element. The process of impregnating involved applying liquid DDA to the back side of the WP using a manual coating apparatus. Four distinct DDA ratios, ranging from 0% to 20% by mass of WP, were applied. The chemical compatibility of the developed WP/DDA composite was explored using Fourier Infrared Spectroscopy (FTIR). The thermal energy storage (TES) properties were assessed through Differential Scanning Calorimeter (DSC) analysis, and the thermo-regulative performance of the WP/DDA composite was evaluated in laboratory-scale test rooms under real weather conditions. The DSCoutcomesexposed that melting temperature and latent heat capacity of WP/DDA were 21.78 °C and 26.9 J/g, respectively.The thermoregulation tests showed that the prepared WP/DDAsignificantly reduce interior room temperature fluctuation and can maintain indoor temperature longer in comfortable temperature ranges. The largest difference between the reference room and test room was observed to be about 2℃. The room temperature was cooler for about 9 h 53 min during day times for the DDA case.The results designated that the developed WP/DDA composite could be evaluated as a promising new kind of building wall covering element for reducing the cooling load of room.

Nanofibrous membranes with hydrophobic and thermoregulatory functions fabricated by coaxial electrospinning

AbstractIn the face of changing outdoor environments, it is necessary for us to develop advanced textiles with thermal regulation and hydrophobic properties. In order to create a fabric with both temperature control and waterproof properties, the study adjusted the ratio of polystyrene (PS) and polyvinylidene fluoride (PVDF) to produce nanofiber membranes with excellent morphology and dirt resistant properties. Furthermore, the hydrophobicity of the nanofibers was further improved by adding SiO2 to the spinning solution. Based on this, a core solution of octadecane (Oct) was used to give it thermal regulation functionality through coaxial electrospinning technique. The resulting composite nanofiber membrane exhibited excellent hydrophobicity and thermal regulation performance. The measurement results obtained from Differential Scanning Calorimetry (DSC) indicate that the maximum Oct encapsulation rate of the PS/PVDF/SiO2@Oct nanofiber membrane is 58.36%. The latent heat of the composite nanofiber membrane is 148.84 J/g, and the water contact angle (WCA) is 135°. The multifunctional composite nanofiber has great potential for applications in outdoor protective clothing and outdoor electronic device protection.

TC@MF phase change microcapsules with reversibly thermochromic property for temperature response and thermoregulation

A series of reversibly thermochromic phase-change microcapsules (TC@MF), demonstrating excellent energy storage and release properties, were synthesized using melamine formaldehyde resin (MF) encapsulated ternary complex consisting of crystal violet lactone (CVL), 2,2-Di-(4-hydroxyphenyl) propane (BPA), and n-hexadecanol. The microstructure, chemical composition, thermal storage capacity, thermal cycling durability, discoloration effect, and thermal regulation performance of TC@MF with different core contents were investigated in detail. With core contents gradually increasing, the chromatic aberration values (ΔE) value of TC@MF increased from 38.23 to 71.69, the melting enthalpy (ΔHm) gradually increased from 180.2 J/g to 218.6 J/g while the leak-proof performance decreased gradually. The TC@MF-2 with the best comprehensive performance has exhibited superior latent heat storage (ΔHm = 192.2 J/g), high chromatic aberration values (ΔE = 57.31), and well leak-proof properties (5.61 %). Furthermore, the thermal performance, morphology, and reversible color reliability of TC@MF-2 remained stable through 100 thermal heating and cooling cycles, demonstrating excellent thermal cycling stability. In summary, such multifunctional microcapsules can directly reflect the energy saturation and depletion states in phase change material applications through color changes. That might be conducive to expanding the value of its practical application in the field of latent heat energy storage, including smart fabrics or fibers, commodity packaging, thermal sensors, reversible thermochromic coatings and solar energy storage, and so on.

Preparation and characterization of oligomeric thermal phase change polyurethane foam

The generation of a large amount of heat during the formation process of polyurethane foam (PU) hinders the large-scale applications of the materials. Phase-change materials (PCM) can be introduced into PU to reduce the amount of heat accumulation inside PU. Silica-based urea-formaldehyde heteroshell phase-change microcapsules (S-MPCM) containing polydopamine were fabricated, followed by the fabrication of a novel composite polyurethane foam (PU/S-MPCM) doped with S-MPCM. The latter was fabricated using 4,4′-diphenylmethane diisocyanate and polyether polyol as the primary raw materials. The results revealed that the modifying effect of polydopamine resulted in the SiO2 layer deposited on the surface of the microcapsules improved the densification of S-MPCM, and the encapsulation rate of S-MPCM was 76.5 %, and the enthalpy of melting was 162.4 J/g. The compatibility of S-MPCM with the foam was also further improved, increasing the toughness of the composite foam and maximizing its retention of morphology after compression testing. The maximum internal temperature of the composite foam blended with 10 % S-MPCMs was reduced to 53.7 °C, showing excellent thermal regulation performance. The oligomeric thermal phase change polyurethane foam prepared in this study can be considered for applications such as building insulation and mine grouting.

Thermal management ability and flame retardancy of silicone rubber foam filled with flame retardant phase change capsules

A novel phase change capsule with layered double hydroxide (LDH) modified SiO2 shell (named M-EPCM) was designed and prepared, which was used to improve the thermal regulation performance and flame retardancy of silicone rubber foam (SRF). The SRF-3 composite containing 18 wt% M-EPCM presented greatly improved thermoregulation ability, and excellent thermal reliability even after 100 cycles. Besides, SRF-3 also exhibited excellent flame retardancy, with the limiting oxygen index exceeding 31.0%, reduced peak heat release rate (36.4%) and low total smoke yield (13.8 m2). The flame retardant mechanism analysis revealed that barrier effect, catalytic crosslinking and polyaromatic reaction provided by LDH played an important role. Moreover, SRF composites have outstanding mechanical properties, especially SRF-3 which showed a 150% and 85% increase in tensile strength and compression strength compared with pure SRF, respectively. This article provides a new idea for further application of LDH in the field of thermal management.

Thermal comfort and flame retardant performance of novel temperature-control coatings with modified phase change material microcapsules

Organic phase change material (PCM) is considered to be promising for building energy efficiency, as it can be directly incorporated into matrix resin to impart thermal storage capacity after being encapsulated in a shell to form phase change material microcapsule (EPCM). However, existing studies have shown that the encapsulation of organic shell materials negatively affects the inherent thermal storage efficiency of PCM and increases its fire hazard. Towards efficient utilization of the thermal storage efficiency of organic PCM and reduction of its fire hazard when applied to building insulation coatings, we decorated halloysite nanotube (HNT) with P, N component (p-HNT) and embedded it into EPCM (p-h-EPCM), which integrated the high thermal conductivity and flame retardancy of p-HNT and developed a high-performance EPCM for thermal regulation coatings. Specifically, p-h-EPCM possesses exceptional thermal stability and has an enthalpy of 113.21 J/g. After mixing p-h-EPCM into epoxy resin (EP/p-h-EPCM), we further investigated its flame-retardant effect and temperature control performance in practical applications. The cone calorimeter (CCT) showed that EP/p-h-EPCM was 35.7 % lower in the peak of heat release rate (pHRR) and 18.97 % lower in the total heat release (THR) compared to the epoxy resin (EP) that incorporated the same mass of EPCM (EP/EPCM). Moreover, the small room test and thermal imager test results showed that EP/p-h-EPCM had the mildest temperature fluctuations of 8.68 °C and 5.23 °C when heating/cooling, respectively. Considering the favorable flame retardant effect and energy-efficient thermal regulation performance, the obtained p-h-EPCM has a broad prospect in the practical application of building temperature-control coatings.

Mechanically Switchable Multifunctional Device for Regulating Passive Radiative Cooling and Solar Heating.

Energy consumption during cooling and heating poses a great threat to the development of society. Thermal regulation, as switchable cooling and heating in a single platform, is therefore urgently demanded. Herein, a switchable multifunctional device integrating heating, cooling, and latent energy storage was proposed for temperature regulation and window energy saving for buildings. A radiative cooling (RC) emitter, a phase-change (PC) membrane, and a solar-heating (SH) film were connected layer by layer to form a sandwich structure. The RC emitter exhibited selective infrared emission (emissivity in the atmospheric window: 0.81, emissivity outside the atmospheric window: 0.39) and a high solar reflectance (0.92). Meanwhile, the SH film had a high solar absorptivity (0.90). More importantly, both the RC emitter and the SH film displayed excellent wear resistance and UV resistance. The PC layer can control the temperature at a steady state under dynamic weather conditions, which could be verified by indoor and outdoor measurements. The thermal regulation performance of the multifunctional device was also verified by outdoor measurements. The temperature difference between the RC and SH models of the multifunctional device could reach up to 25 °C. The as-constructed switchable multifunctional device is a promising candidate for alleviating the cooling and heating energy consumption and realizing energy saving for windows.

Thermal Regulation Performance of Shape-Stabilized-Phase-Change-Material-Based Prefabricated Wall for Green Grain Storage.

In order to meet the great demand for green grain storage and low carbon emissions, paraffin, high-density polyethylene (HDPE), and expanded graphite (EG) were used to produce shape-stabilized phase change material (SSPCM) plates, which were then used to reconstruct building walls for existing granaries. A new type of SSPCM plate was then prefabricated with different thermal conductivities and a high latent heat. This plate could be directly adhered to the existing granary walls. In order to evaluate the thermal regulation performance of these phase change granary walls, experiments and numerical methods were established, specifically for the summer condition. The thermal behavior of the SSPCM granary wall was compared with that of the common concrete granary wall to obtain the optimal parameters. It was concluded that increasing the thickness of the SSPCM layer can reduce the temperature rise of the wall. However, the maximum latent heat utilization rate and energy storage effects were obtained when the SSPCM thickness was at an intermediate level of 30 mm. The thermal conductivity of the SSPCM had a controversial effect on the thermal resistance and latent heat utilization behaviors of the SSPCM. Considering the temperature level and energy saving rate, a 30 mm thick SSPCM plate with a thermal conductivity of 0.2 W/m·K provided a superior performance. When compared to the common wall, the optimized energy-saving rate was greatly enhanced by 35.83% for the SSPCM granary wall with a thickness of 30 mm and a thermal conductivity of 0.2 W/m·K.

Construction of layered double hydroxide-modified silica integrated multilayer shell phase change capsule with flame retardancy and highly efficient thermoregulation performance

Current energy problems have driven the development of thermal storage technology based on phase change materials (PCMs). However, the leakage and flammability of organic PCMs appeared as troublesome agendas that deserve attention. In this article, the strategy of constructing phase change capsules with paraffin wax (PW) core and multilayer shell was proposed aiming to address the above issues. For the integrated multi-layer shell, silica (SiO2) acts as initial layer to encapsulate the PW core, and then tannic acid (TA) was creatively taken to bridge the subsequent flame retardant layered double hydroxides (LDH) layer on the surface of the silica shell, and polyvinyl alcohol (PVA) layer was further introduced to improve the compatibility of phase change capsules with polymer matrix. Characterization of chemical structure and morphology confirmed that phase change capsules with LDH modified silica multilayer shell (M-EPCMs) was successfully prepared. The results indicated that M-EPCMs, particularly the representative M-EPCM-5, possessed outstanding thermal stability, excellent leak proofness, good thermal regulation performance as well as long-term cycling stability. Importantly, M-EPCM-5 with the thickest LDH layer can self-extinguish when exposed to fire, and especially can keep the integrity of its shell without breakage after being heated at high temperature. Furthermore, the silicone rubber foam (SRF) composite containing M-EPCM-5 can reach UL-94V-1 level, indicating the flame retardancy of SRF matrix was improved significantly. The possible flame retardant mechanism revels that LDH can not only accelerate the formation of dense ceramic protective layer in condensed phase, but also release non-combustible gases (H2O, CO2) in gas phase, thus improving the fire retardancy of M-EPCMs. Therefore, the construction strategy proposed in this article represents a powerful means to improve flame retardancy and prevent leakage of phase change capsules at the same time, which will greatly expand the application scope of PCMs.

Microencapsulated phase change n-Octadecane with high heat storage for application in building energy conservation

A novel type of microencapsulated phase change materials (microPCMs) with n-Octadecane core shelled by styrene–divinylbenzene copolymer were synthesized by the suspension polymerization. The morphologies and chemical compositions of the microPCMs with four different shell-to-core ratios were analyzed via the scanning electron microscopy and Fourier transform infrared spectroscopy. Based on the measurements from the thermogravimetric analyzers and differential scanning calorimetry, the thermal characteristics of the different microPCMs were analyzed. The results show that the sample microPCMs with 2:1 shell-to-core ratio (microPCM3) has good thermal stability and high heat storage capability, with melting enthalpy and encapsulation efficiency measured at 111.5 ± 0.7 J/g and 51.4 ± 0.7 %, respectively, which are the highest among all the prepared samples. The initial weight loss temperature of the microPCM3 increases to 160.5 ℃ compared to 115.5 ℃ for the pure n-Octadecane. Furthermore, we prepared four different building boards with different microPCM3 contents (0, 10, 20, or 30 wt%) in cement matrix. Compared to the conventional building material, the board with 30 wt% microPCM3 can store 67.82% more heat energy in the typical temperature range of 10–50 °C. We investigated the passive cooling and heating effects of the boards under extreme temperature conditions (10–70 °C), as well as their thermal regulation performance under multiple consecutive thermal cycling experiments. Compared with the cement board without addition of microPCM3, the board with 30 wt% microPCM3 has reduced temperature fluctuation by 59.0% with maximum temperature fluctuation only 23.5 °C. It has shown excellent thermal regulation and thermal insulation properties and is of great application potential in energy-saving buildings.

Passive thermal regulation with 3D printed phase change material/cellulose nanofibrils composites

Application of phase change materials (PCM)-containing composite represents a promising passive thermal control strategy to provide indoor thermal comfort without using powered equipment. Yet, the trade-off between high thermal storage density and good thermal stability is the major obstacle that restricts the thermal regulation performance of the current PCM-containing products. This study proposed a facile approach to prepare PCM/cellulose nanofibrils (CNF) ink for 3D printed composite monolith, with very high PCM loading, good thermal stability, and robust mechanical properties. By incorporating a small amount of CNF gel as the stabilizer and viscosity modifier, the CNF-microencapsulated paraffin (model PCM) obtained essential printability to construct tailorable structure using Direct Ink Writing technology. After ice templating and freeze drying, the microencapsulated PCM particles were in-situ embedded in a CNF-assembled scaffold, forming a PCM/CNF composite. The lightweight nature of such scaffold (35.0 mg/cm3 for pure CNF matrix) endowed the composite monolith with high PCM loading (up to 82% with respect to the composite) and high thermal storage capacity (up to 153 J/g). Due to the 3D-interlinked CNF matrix and the coated CNF on PCM particles, the composite monolith not only exhibited high Young's modulus of up to 1.14 MPa but also showed exceptional thermal stability with negligible variation in microscopic morphology and thermal storage capacity, after high temperature conditioning at 80 °C for 30 h.