Solid Phase Change Material Research Articles

Single‐step preparation of intrinsic solid–solid phase change materials with excellent anti‐leakage and form‐stable performance

AbstractPhase change materials (PCM) often encounter severe problems of leakage and shape collapse concerns. Chemical modification methods, utilizing chemical bonds to bind phase change molecular chains, have the potential to address the above‐mentioned problems radically. However, this approach often entails the use of expensive raw materials and complex processes. Therefore, a simple one‐pot preparation method had been reported using earth‐abundant and inexpensive octadecyl methacrylate (OMA) and 1,6‐hexanediol diacrylate (HD) as raw materials to prepare PCM with a molecular structure of cross‐linked polymer main chains and phase change side chains through free radical polymerization. Owing to the three‐dimensional polymer main chain structure, it exhibited excellent leakage‐proof performance, maintaining its form‐stable nature at 70°C with no obvious leakage observed during the phase change process, confirming it to be an excellent intrinsic solid–solid PCM (SSPCM). Additionally, the introduction of the cross linking segment significantly improves its thermal stability, and the 50% degradation temperature increased significantly from 228.8 to 355.9°C. Moreover, the latent heat increased with the decrease of the crosslinking density until the molar ratio of HD/OMA was reduced to 1/40 and then tended to reach constant. At the optimal ratio the latent heat of SSPCM can reach 88.23 J g−1. Excessive crosslinking density will affect the stacking tightness of molecular chains during the crystallization process, thereby reducing the latent heat.

Bis(dialkylammonium)-based hybrid organic–inorganic ionic materials as solid–solid phase change materials

The application of phase change materials (PCMs) in thermal energy storage (TES) systems is often restricted by challenges such as volume expansion, phase segregation, stability issues and potential leakage, particularly prominent in conventional solid–liquid PCMs. In response to these limitations, solid–solid PCMs have emerged as a promising alternative, garnering increasing attention. While both organic and inorganic solid–solid PCMs have been extensively studied, hybrid organic/inorganic materials represent a distinct class of solid–solid PCMs that have recently garnered significant interest due to their inherent properties such as high thermal stability, non-flammability or long cycle life. Organic-inorganic layered perovskites are emerging as potential good solid–solid PCMs as they present energetic solid–solid transitions and high thermal stability. In this work we propose the synthesis and thorough thermal characterization and cyclability of a series of new hybrid organic–inorganic ionic materials based on n-dialkylamines of different lengths (C8, C10, C12 and C18) with general formula of the type 2[(CnH2n+1)2NH2][MX4], using three different tetrachlorometalates anions ([FeCl4]2-, [MnCl4]2- and [CuCl4]2-). Among the new ionic materials prepared six of them have shown solid–solid transition enthalpies higher than 100 J/g. In particular, the 3 bearing the secondary n-dioctadecylamines as cations have shown unprecedent solid–solid transitions enthalpies ca. 90 °C, for this kind of ionic materials of 167.5 J/g, 157.7 J/g and 146.9 J/g for [DODA]2[MnCl4], [DODA]2[CuCl4] and [DODA]2[FeCl4] respectively. In addition, the latter ionic materials have undergone reliability tests showing excellent performance up to 500 heating/cooling cycles.

Magnetically- regulated close contact melting for high-power-density latent heat energy storage

Rapid melting of solid-liquid phase change materials (PCMs) is critical to the high-power-density latent heat energy storage and efficient thermal management. The pressure-enhanced close contact melting is seen as a promising method because of the suppressed heat transfer resistance between the heating surface and the melt front during thermal charging, but it remains a key challenge how to tactfully apply external pressure for a practical device. Herein, we present a magnetically-regulated close contact melting strategy for rapid melting of PCMs from the perspective of the practical application. In this method, a PCM and a permanent magnet are contained inside a highly thermally conductive vessel, and the magnet regulated by another one can push the solid PCM toward the heating surface. Consequently, the superheated molten PCM can be instantly removed from the heating surface due to the magnetic force so as to achieve the suppressed thermal resistance. The temperature-control performance of paraffin wax is evaluated under various applied external forces and heat loads. Experimental results indicate that the heating surface temperature can be controlled near the melting temperature of PCM even under a relatively high heating flux. With applying the external pressure of 900 Pa, the average heat transfer resistance is reduced to lower than 4.5 × 10−4 K·m2·W−1. Finally, a closed thermal management device is fabricated and measured by using a graphite vessel to encapsulate the magnet and the PCMs such as paraffin and low-melting-point alloy. This device demonstrates good recyclability for repeated thermal charging/discharging. Our work provides a new method to develop the practical thermal management device based on pressure-enhanced close contact melting.

Mechanically strong, healable, and recyclable supramolecular solid–solid phase change materials with high thermal conductivity for thermal energy storage

Conventional polymeric solid–solid phase change materials (SSPCMs) have garnered significant attention in the development of state-of-the-art latent heat storage (LHS) systems. However, the industrial application of polymeric SSPCMs is compromised by inferior mechanical properties and intrinsic low thermal conductivity. In addition, they are unable to be recycled and self-healed due to permanently cross-linked structures. In this study, a series of healable and recyclable supramolecular SSPCMs (PEG4K-Bx-PEG6K), possessing robust tensile strength (∼22.90 MPa), excellent strain-at-break (∼733.62 %), and high toughness (∼120.05 MJ/m3), are designed and developed by incorporating dynamic boroxines and hydrogen bonds. Because of the reversibility of dynamic boroxines and hydrogen bonds, the PEG4K-Bx-PEG6K was able to be healable and conveniently processed into packaging bag. More importantly, the PEG4K-Bx-PEG6K also possessed high thermal storage capacity (98.03 J/g), and excellent thermal shape memory capability. To achieve efficient heat transfer, an orientated solar thermal composite with high thermal conductivity was fabricated by compression-induced repetitive stacking of oriented graphene nanosheets (GNs) layers in PEG4K-Bx-PEG6K. Thanks to the efficient heat conduction of oriented GNs layers in the composite, the directional thermal conductivity of composite was up to 3.639 W/mK at 5 wt% loading of GNs. Combining the above excellent heat conduction, the solar thermal composite developed in this work offered efficient solar thermal conversion, fast transportation and storage of the harvested thermal energy.

Evaluation of wavy wall configurations for accelerated heat recovery in triplex-tube energy storage units for building heating applications

Efficient thermal energy storage (TES) is crucial for integrating intermittent renewable energy sources and managing fluctuations in energy supply and demand. Among TES methods, latent heat TES (LHTES) using phase change materials (PCMs) is highly promising due to its high energy storage density and nearly isothermal operation during phase transitions. However, the inherently low thermal conductivity of PCMs hinders heat transfer rates, negatively impacting charging and discharging performance. This study investigates novel wavy channel geometries for the PCM container in a triplex-tube LHTES unit to enhance heat transfer and improve solidification rates during the discharge process. A comprehensive computational model based on the enthalpy-porosity method is developed to simulate the PCM (paraffin wax RT35) solidification inside wavy channels with sinusoidal, zigzag, and step-function profiles. The effects of channel geometry, heat transfer fluid (HTF) velocity, and inlet temperature on solidification rate and heat recovery are systematically evaluated. Results demonstrate that the step-function geometry significantly accelerates solidification compared to straight channels, reducing discharge time by 65.1 % and increasing heat recovery rate by 147.9 %. Decreasing waviness width from 15 mm to 5 mm further reduces solidification time by 70.1 %, while increasing waviness height from 5 mm to 15 mm leads to a 74.4 % reduction. Moreover, increasing HTF flow from Re = 250 to 1000 enhances heat recovery by 92.3 %, and lowering inlet temperature from 20 °C to 10 °C improves it by 76.9 %. The findings provide valuable insights for designing efficient LHTES units with wavy channel geometries for renewable energy integration and thermal management applications.

X-ray computed tomography analysis of calcium chloride hexahydrate solidification

Latent Thermal Energy Storages (LTESs) are receiving increasing interest, since they offer many advantages to the field of Thermal Energy Storages (TESs), such as a nearly isothermal solid–liquid phase transition and a high energy storage density. To boost the transition towards a climate-neutral future, a lot of work is surely needed on Phase Change Materials (PCMs) which are used inside LTESs. Salt hydrates, a particular class of PCMs, are very attractive in terms of cost and volumetric latent enthalpy but present drawbacks that still limit their effective deployment in real applications, such as supercooling and phase separation (or segregation). The current work assesses the suitability of X-ray Computed Tomography (XCT) as a novel technique in the field of LTESs to study the solidification of phase-change materials. In this study, calcium chloride hexahydrate (CaCl2·6H2O) is chosen as a representative PCM and the results derived are shown to be repeatable. For the first time, the direct measurement of the volumetric liquid fraction is correlated to temperature measurements allowing for the visualisation of supercooling and the validation of an enthalpy-porosity numerical model, which could be useful in the design of LTES. XCT methodology offers unmatchable features as compared to the other method to measure the volumetric liquid fraction. Given its accuracy and the rigorous protocol, it can be considered as a benchmark for new liquid fraction measurement technologies but it also permits to study how the different PCMs melt and solidify, giving new insights on the mechanisms at the basis of the most crucial challenges, among those: subcooling, segregation, and metastable phase change.

Applying isovolumic steam capsule as new thermal energy storage unit

In order to make up the inefficiencies of liquid–solid phase change material (PCM) such as low latent heat and low heat transfer rate, the possibility of adopting water steam as the phase change material is explored. Although great volume change occurs during the gas–liquid phase-changing, the specific latent heat is at least one order of magnitude larger than that of liquid–solid phase-changing. To minimize the adverse effect of the great volume change during vaporization or condensation, the steam can be accommodated inside sealed vessel with sturdy shell. In this study, an isovolumic steam capsule (ISC) was made by filling a cylinder with a small amount of liquid water and then heated and boiled to extinguish the non-condensable gas (NCG) before sealing it. Thermodynamic analysis shows the thermal energy contained in the isovolumic steam capsule per unit volume increases in approximately an exponential manner with the increase of temperature due to the evaporation of liquid, and can reach several times that of liquid–solid phase change material, demonstrating great potential as energy storage material. The heat transfer experiments show that the energy charging and discharging rates increase with the temperature difference. There exists thermodynamic non-equilibrium during heat transfer and the deviation from saturation enlarges with increasing temperature difference and non-condensable gas concentration. For both charging (vaporization) and discharging (condensation), a higher non-condensable gas concentration in the steam exhibits larger heat transfer rate in the beginning, but smaller heat transfer rate in the later stage. The mechanism of vaporization and condensation in the isovolumic steam capsule awaits to be further clarified.

Super‐liquid‐repellent thin film materials for low temperature latent heat thermal energy storage: A comprehensive review of materials for dip‐coating

AbstractWhen discharging latent heat thermal energy storage (LHTES) systems, performance is influenced by the formation and adherence of a solid layer of phase change material (PCM) on heat eXchange (HX) surfaces. Super‐liquid‐repellent thin films (STFs) may be able to reduce solidifying PCM adhesion on HX surfaces during discharging, delay PCM solidification to lower temperatures, and by modifying nucleation sites potentially enable long‐term seasonal thermal storage. Techniques employed previously to fabricate sintered polymeric STF coatings include chemical vapour deposition, dip‐coating, spray‐coating, spin‐coating, layer‐by‐layer (LbL) assembly, sol‐gel, anodizing, electrodeposition, electrospinning, so on. Dip‐coating is considered attractive for fabricating thin films on simple and complex surface geometries due to process maturity, scalability, flexibility and cost‐effectiveness. To identify suitable materials for preparing STFs on metal HX surfaces using the dip‐coating process, more than 200 journal articles published in English during the period 2010 to 2022 were reviewed and the potential role of STFs in LHTES applications was assessed. The review identified key areas and applications stimulating STF material developments and formulations. The dip‐coating of potential STF materials was classified under three major themes driving current research and development (R&D) activities, that is, high performance thin films, eco‐friendly thin films and fundamental research formulations. This review provides a platform from which to develop coatings and HX systems to enable the cost‐effective implementation of STFs for improved heat transfer in future mobile/stationery LHTES systems.

A thermal management design using phase change material in embedded finned shells for lithium-ion batteries

Phase change material (PCM) has recently been regarded as a promising thermal management means for lithium-ion (Li-ion) batteries. However, solid-liquid phase change of many current PCMs occurs in a narrow temperature range, and the cooling performance of their liquid phase is rather poor. To tackle these issues, this article presents a battery thermal management (BTM) design which injects PCM into an aluminum shell around each cell, and machines the shell inner surfaces into a row of straight rectangular fins immersed into the PCM and its outer surfaces into a plain-fin shape exposed in the air. In the mild thermal conditions, the finned shells of two adjacent cells can be embedded and passive PCM cooling is employed. Once the PCM completely melts, the shells will move apart and an airflow will be driven through the gap between them. The BTM design can also protect Li-ion batteries in a freezing environment, by taking advantage of PCM solidification when the finned shells return to their embedded configuration. A series of experiments were conducted to examine its effectiveness on two 50Ah lithium nickel cobalt manganese oxide (NCM) prismatic batteries, which were discharged at a capacity-rate of 2C and at room temperatures of T0=25∘C, 40∘C and −10∘C. It is shown that in the battery discharge at T0=25∘C, PCM in the embedded finned shells effectively reduced the average battery-surface temperature (T¯) and the maximum temperature difference (ΔTmax) by 21% and 36.7%, respectively, compared to bare batteries. At T0=40∘C, this BTM design successfully limited the growth of T¯ to 9.0∘C and led to ΔTmax no more than 1.5∘C. As to the low-temperature scenario, it maintained the batteries at temperatures above T0 for 55.2% longer than those without any BTM protections. Its cooling performance was also compared with that of the conventional liquid-cooling scheme using a bottom serpentine-channel cooling plate. All these results clearly demonstrate that the BTM design in this article can compensate for the deficiencies of conventional PCM-based BTM schemes. Regardless of whether the PCM phase change is available, it has well coped with different thermal management demands of Li-ion batteries.

A Comprehensive Parametric CFD Investigation on Packed Bed Thermal Energy Storage System with Encapsulated Solid–Solid Phase Change Materials in Discharging Mode

A Comprehensive Parametric CFD Investigation on Packed Bed Thermal Energy Storage System with Encapsulated Solid–Solid Phase Change Materials in Discharging Mode

A self‐regulated phototheranostic nanosystem with single wavelength‐triggered energy switching and oxygen supply for multimodal synergistic therapy of bacterial biofilm infections

AbstractThe exploration of antibiotic‐independent phototherapy strategies for the treatment of bacterial biofilm infections has gained significant attention. However, efficient eradication of bacterial biofilms remains a challenge. Herein, a self‐regulated phototheranostic nanosystem with single wavelength‐triggered photothermal therapy (PTT)/photodynamic therapy (PDT) transformation and oxygen supply for multimodal synergistic therapy of bacterial biofilm infections is presented. This approach combines a eutectic mixture of natural phase‐change materials (PCMs) and an aggregation‐induced emission (AIE) phototheranostic agent TPA‐ICN to form colloidally stable nanopartcicles (i.e. AIE@PCM NPs). The reversible solid−liquid phase transition of PCMs facilitates the adaptive regulation of the aggregation states of TPA‐ICN, enabling a switch between the energy dissipation pathways for enhanced PDT in solid PCMs or enhanced PTT in liquid PCMs. Additionally, oxygen‐carrying thermoresponsive nanoparticles are also introduced to alleviate the hypoxic microenvironment of biofilms by releasing oxygen upon heating by AIE@PCM NPs with enhanced PTT. The nanosystem exhibits outstanding therapeutic efficacy against bacterial biofilms both in vitro and in vivo, with an antibacterial efficiency of 99.99%. This study utilizes a self‐regulated theranostic nanoplatform with adaptive PTT/PDT transformation via the phase transition of PCMs and heat‐triggered oxygen release, holding great promise in the safe and efficient treatment of bacterial biofilm infections.

Selection of phase change material for latent heat thermal energy storage using a hair-pin heat exchanger: Numerical Study

Abstract Phase change materials (PCMs) are promising for storing thermal energy as latent heat, addressing power shortages. Growing demand for concentrated solar power systems has spurred the development of latent thermal energy storage, offering steady temperature release and compact heat exchanger designs. This study explores melting and solidification in a hairpin-type heat exchanger (HEX) using three PCMs (RT 50, RT 27, and RT 35). A 3D model of the hairpin type heat exchanger (HEX) is drawn using Ansys-workbench. High-temperature fluid/Low-temperature fluid (HTF/LTF) with Stefan numbers (0.44, 0.35, and 0.23) flows through the inner pipe to charge the outer pipe's PCM. The Enthalpy-porosity model is used to study the melting and solidification of various PCMs, and the results were compared. Also, individual thermophysical properties that affect the heat transfer during the melting and solidification process have been discussed. It is observed that low thermal conductivity material with high latent heat is preferred for cold climates. In this study, RT 27 excels in cold climates due to extended solidification time, while RT 50 is effective in tropical regions due to its high melting points and lower latent heat.

Morphology changes of polymer solid-solid phase change material in high-viscosity modified asphalt (HVMA) and its influence on the properties of HVMA

Asphalt pavement has excellent performance, but the asphalt binder is a temperature-sensitive material, which not only easily causes high-temperature distress, but also exacerbates the “urban heat island effect”. One possible method to solve this problem is to use phase change material (PCM) in the asphalt mixture, in which polymer solid-solid phase change material (PSSPCM) is one of widely used PCM. If the PSSPCM can be used in high-viscosity modified asphalt (HVMA), the high-performance modified asphalt with temperature regulation function can be obtained. However, the morphology of PSSPCM may change under the high mixing temperature of HVMA, which may also influence the properties of PSSPCM/HVMA composite. This paper selected one typical PSSPCM to investigate the morphology changes of solid-solid phase change material in HVMA and its influence on the properties of HVMA. The change of morphological and thermal property of PSSPCM in the high-temperature preparation were characterized by scanning calorimeter tests, thermogravimetric tests and heating tests, the physical, rheological and temperature regulation properties of PSSPCM/HVMA were also investigated. Test result shows that, the PSSPCM melted in HVMA at high mixing temperatures condition. However, when added in smaller contents of PSSPCM, the melted PSSPCM could uniformly distribute in the HVMA and the polymer network structure was formed. The melted and distributed PSSPCM in HVMA still had favorable temperature regulation function. The temperature regulation range of PSSPCM during the heating process and cooling process is maximum 3.8°C and 2.9°C respectively. Notably, the PSSPCM/HVMA has great high-temperature properties and favorable low-temperature properties. This study has reference value for developing the high-performance modified asphalt with temperature regulation function.

Approximate analytical solution for solidification of PCM in cylindrical geometry with temperature‑dependent thermal conductivity-perturbation method

The Solidification process of Phase change materials inside cylindrical enclosures is analyzed and analytical solutions are derived to determine the positions of the interfaces at different time intervals. In this current investigation, we address the scenario involving temperature-dependent thermal conductivity. For the first time, we employ perturbation techniques to analytically derive the dimensional temperature for both phases. Our study specifically incorporates a linear model to account for the variation in thermal conductivity with temperature. The results show that the duration of complete solidification relies on the Stefan number. As these parameter is augmented, the total solidification time of the cylinder diminishes and escalates, respectively. Furthermore, it has been observed that an augmentation in the thermal conductivity of the phase change material (PCM) leads to a swifter solidification process.

Design, analysis, and testing of a prototype-scale latent heat thermal energy storage (LTES) system

A parametric analysis was performed to design a prototype-scale latent heat thermal energy storage (LTES) system using commercial grade hexahydrate calcium chloride as phase change material (PCM) in a staggered tube array configuration, placed horizontally. The study involved numerical analysis of melting and solidification processes of the PCM within the tube array, considering transient two-dimensional Navier-Stokes equations and a Realizable k-ɛ turbulence model to predict fluid flow and heat transfer. The enthalpy-porosity technique was used to model PCM melting and solidification. The study included a comparison between numerically predicted and experimentally obtained air temperatures at the tube array outlet, as well as PCM temperatures. This comparison revealed an excellent level of agreement. Additionally, the study compared the pressure drop within the array and the average peripheral heat transfer coefficient calculated from the numerical results to the well-established Zukauskas correlation. The resulting design successfully met the predefined performance criteria: achieving a cooling effect of 4 °C for a four-hour duration while maintaining a pressure drop of <100 Pa. The proposed prototype-scale tube array design can be efficiently cooled down and PCM frozen overnight. The energy storage density of the system falls within the range of 22 to 27 kWh/m3.

Parametric study of a scraped surface heat exchanger for latent energy storage for domestic hot water generation

In this work, a parametric study of a Scraped Surface Heat Exchanger (SSHE) for solar Latent Thermal Energy Storage (LTES) has been conducted. The primary challenge in Phase Change Material (PCM) heat exchangers is the formation of a solid layer along the heat transfer surfaces during the latent energy release phase. This reduction in the energy release rate is resolved through the scraping of the solidified PCM, making SSHE systems suitable for domestic hot water generation. Experiments have been performed to evaluate the influence of various operational parameters, including the heat transfer fluid (HTF) mass flow rate, the phase change characteristics of the PCM, the temperature difference between the HTF and the PCM, and the scraping velocity. It has been observed that a HTF Reynolds number (Re) of 100 will require three times more time compared to Re = 600. Moreover, the significance of maintaining a HTF to PCM differential temperature between 20 °C and 25 °C has been experimentally verified to improve the PCM solidification process. Furthermore, the existence of a critical scraping frequency has been demonstrated, beyond which increasing the frequency does not yield to significant improvements in energy extraction. Finally, a correlation has been proposed to predict solidification time as a function of the non-dimensional operational parameters involved, where 95 % of the results fall within an interval of 10 %.

Numerical investigation and optimisation of solid–solid phase change material composite-based plate-fin heat sink for thermal management of electronic package

Phase Change Material based Thermal Management Systems show promise in electronic packaging systems for safe operation, acting as a thermal storage element to prevent sudden temperature surges, enhancing operational time and mitigating electronic system failures. Therefore, the meticulous design of a solid–solid phase change material (SSPCM) based heat sink with fins is imperative for effective electronic thermal management by improving its safe operational time. This study performs a numerical analysis of two-dimensional transient heat transfer for the SSPCM-based plate-fin heat sink using the modified enthalpy porosity method, where the plate fins serve as Thermal Conductivity Enhancers (TCEs). Neopentyl glycol with 6% (w/w) Copper oxide nanoparticle is used as the SSPCM composite. Enhancement ratio based on safe operational time at different power levels (2–6 W) with different percentages of TCE and fin count recorded variation from 1.32 to 13.7. The TCE integration is more effective at higher power levels. The optimisation of SSPCM-based heat sink design for maximum safe operational time is accomplished through Response Surface Methodology. The significance of the TCE fraction, number of fins, heat generation rate, and interaction effects over the safe operational time are observed. The correlation for safe operational time as a function of TCE volume fraction, fin count and heat generation rate is developed. TCE volume fraction possesses the highest influencing factor over safe operational time at lower and higher power levels compared to fin count. At 2 W and 6 W, a maximum change in safe operational time is observed from 72.7% at 2 W to 83.45% at 6 W. The heat sink with 0.262 volume fraction of TCE and 11 fins is the optimised design that can provide the desirable safe operational time for the tested range of power levels.

Phase Engineered Composite Phase Change Materials for Thermal Energy Manipulation.

Phase change materials (PCMs) present a dual thermal management functionality through intrinsic thermal energy storage (TES) capabilities while maintaining a constant temperature. However, the practical application of PCMs encounters challenges, primarily stemming from their low thermal conductivity and shape-stability issues. Despite significant progress in the development of solid-solid PCMs, which offer superior shape-stability compared to their solid-liquid counterparts, they compromise TES capacity. Herein, a universal phase engineering strategy is introduced to address these challenges. The approach involves compositing solid-liquid PCM with a particulate-based conductive matrix followed by surface reaction to form a solid-solid PCM shell, resulting in a core-shell composite with enhanced thermal conductivity, high thermal storage capacity, and optimal shape-stability. The core-shell structure designed in this manner not only encapsulates the energy-rich solid-liquid PCM core but also significantly enhances TES capacity by up to 52% compared to solid-solid PCM counterparts. The phase-engineered high-performance PCMs exhibit excellent thermal management capabilities by reducing battery cell temperature by 15°C and demonstrating durable solar-thermal-electric power generation under cloudy or no sunshine conditions. This proposed strategy holds promise for extending to other functional PCMs, offering a compelling avenue for the development of high-performance PCMs for thermal energy applications.

Performance of a rotating latent heat thermal energy storage unit with heat transfer from different surfaces

Due to the rapid growth in the demand for fast and efficient latent heat thermal energy storage system, multiple heat transfer enhancement techniques have been proposed and widely investigated. Actively or passively, rotation of the energy storage unit affects the internal natural convection and the heat transfer performance. Hence, this study is conducted to evaluate the potential of the heat transfer enhancement by rotation. A two-dimensional model with the phase change material filled in the annular space of a double tube energy storage unit is developed. The numerical simulations for the heat transfer through the internal or external surfaces of the annular space are respectively conducted. Both solidification and melting of the phase change material are taken into account by the enthalpy-porosity method. According to different heat transfer surfaces and the occurrence of solidification or melting, four arrangements are formed. It is found that the rotation of the thermal energy storage unit can reduce the solidification time as high as 46 % compared to its still counterpart, but variation of the rotation speed only produces a minor influence. The effect of rotation on the melting depends on the heat transfer direction (or surface). When the heat is transferred into the solid phase change material through the internal wall, the melting time can be gradually reduced as the rotation speed increases with a maximum of 69 %. However, when the heat is transferred through the external wall, influence of the rotation results in adverse effect. This study can guide the design of innovative high performance latent heat thermal energy storage system containing rotation unit.

A polyurethane solid–solid phase change material for flexible use in thermal management

Phase change materials (PCMs) have received great attention in thermal management of electronic devices due to their high energy storage density and no need for additional energy supply. Yet the leakage problem after phase change limits their application greatly. In this paper, the block copolymerization was used to prepare a novel solid–solid phase change material (SSPCM) with a melting enthalpy of 90.26 J/g, starting pyrolysis at a temperature of more than 300 °C, and its physicochemical and thermal properties remained basically unchanged after 100 heating/cooling cycles. Notably, this SSPCM has excellent shape stability and can be pressed into phase change film with flexibility, thermally induced self-healing capability and recyclability. Finally, we innovatively combined this SSPCM, copper foam (CF), and polyimide tape (PI) to obtain a composite phase change material (CPCM) with both high thermal conductivity (1.1994 W/m·K) and high electrical insulating properties. Thermal management experiment shows that this CPCM has good thermal management performance and can significantly reduce the temperature rise rate of the simulated CPU. The SSPCM prepared in this study shows great potential for application in thermal management of portable electronic devices and flexible wearable electronic devices.