Phase change materials (PCMs) used for the storage of thermal energy as sensible and latent heat are an important class of modern materials which substantially contribute to the efficient use and ...conservation of waste heat and solar energy. The storage of latent heat provides a greater density of energy storage with a smaller temperature difference between storing and releasing heat than the sensible heat storage method. Many different groups of materials have been investigated during the technical evolution of PCMs, including inorganic systems (salt and salt hydrates), organic compounds such as paraffins or fatty acids and polymeric materials, e.g. poly(ethylene glycol). Historically, the relationships between the structure and the energy storage properties of a material have been studied to provide an understanding of the heat accumulation/emission mechanism governing the material's imparted energy storage characteristics. This paper reviews the present state of the art of PCMs for thermal energy storage applications and provides an insight into recent efforts to develop new PCMs with enhanced performance and safety. Specific attention is given to the improvement of thermal conductivity, encapsulation methods and shape stabilization procedures. In addition, the flame retarding properties and performance are discussed. The wide range of PCM applications in the construction, electronic, biomedical, textile and automotive industries is presented and future research directions are indicated.
•Preparation methods of microencapsulated phase change materials were summarized.•Thermal properties of microencapsulated phase change materials were presented and discussed.•Applications of ...microencapsulated phase change materials for thermal storage were analyzed.
Phase change materials (PCM) are characterized by storing a large amount of thermal energy while changing from one phase to another phase (normally solid–liquid states) at a certain temperature. The application of PCM devotes to elevate the global efforts to conserve energy with regard to fast depleting fossil fuels. The selection of supporting materials and encapsulation techniques has crucial effect on the use of the thermal energy released by PCM. The encapsulation method of PCM is an approach to alleviate leakage, phase separation and volume change problems. Microencapsulated phase change materials (MPCM) are one of the most popular techniques to enhance the efficiency in use of resources for thermal energy storage. This work attempts to summarize preparation methods and thermal properties of the MPCM, which helps to better understand the composition and working mechanism of the MPCM. Moreover, the MPCM provide enormous potential to meet the growing demands for applications of cooling and heating in buildings, textiles and MPCM slurry.
•Nano-Encapsulated Phase Change Materials (NEPCMs) are suspended in a base fluid.•Free convection heat transfer of NEPCMs is addressed in a cavity.•Fusion temperature of NEPCM particles is a key ...factor in heat transfer enhancement.•There is an optimum range of fusion temperature leading to maximum heat transfer.•Up to 10% heat transfer enhancement was observed by using NEPCM particles.
Free convective flow and heat transfer of a suspension of Nano Encapsulated Phase Change Materials (NEPCMs) in an enclosure is studied. NEPCM particles are core-shell structured with Phase Change Material (PCM) as the core. The enclosure is a square cavity with top and bottom insulated walls and differentially-heated isothermal vertical walls. The NEPCM particles circulate under natural convection inside the cavity. The PCM cores undergo phase change from solid to liquid and absorb some of the surrounding’s heat in the form of latent heat in the hot region, and release the absorbed heat in the cold region by solidification. The governing equations representing the conservation of mass, flow, and heat of NEPCM suspension are introduced in the form of partial differential equations. The governing equations are transformed into non-dimensional form and solved by the finite element method. A grid check and validation test are performed to ensure the accuracy of the results. The outcomes show that the fusion temperature of NEPCM particles is the key factor affecting the heat transfer enhancement of NEPCMs in the natural convection flow. The enhancement of heat transfer is highly dependent on the non-dimensional fusion temperature, θf, and very good performance can be achieved in the range of ¼ < θf < ¾. Comparing to the base fluid, a relative enhancement of about 10% can be achieved by using NEPCMs at a non-dimensional fusion temperature of ¼.
•A novel cooling system coupling nano emulsion and composite PCM is presented.•Effects of inlet coolant temperature and melting point are numerically studied.•The optimal operating condition for the ...hybrid cooling system is obtained.•Cooling strategy is optimized to enhance the cooling efficiency of PCM.•Tmax and ΔTmax are restrained below 48 °C and 4 °C with low power consumption.
To improve the working performance of lithium-ion batteries under long-term charge–discharge cycles, a delayed cooling system coupling composite phase change material (CPCM) and nano phase change material emulsion (NPCME) is proposed and numerically studied. In this study, optimisation of the dissipate structure was first conducted to obtain the optimal design. Subsequently, the cooling performance of a hybrid battery thermal management system (BTMS) coupling the CPCM and NPCME was comprehensively investigated. The effects of operating conditions such as inlet temperature, CPCM melting point, and NPCME melting point on the cooling performance were separately studied, and the optimal operating conditions were obtained. Finally, the thermal behaviour of the delayed cooling system was studied both in a single charge/discharge operation and continuous charge/discharge cycles. Simulation results indicated that the NPCME/CPCM system offers better cooling performance than the conventional Water/CPCM system, and the NPCME/CPCM cooling system can restrain the target ΔTmax at lower flow rates than Water/CPCM cooling. Compared with the existing hybrid cooling system, power consumption can be significantly reduced without sacrificing the cooling performance. The temperature and temperature difference of the battery pack were below 48 °C and 4 °C in three charge–discharge cycles, respectively, with a CPCM utilisation of 90 vol% and a working time of liquid cooling less than one-quarter of the cycle process.
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Phase change materials (PCMs) can store and release latent heat under the designed phased change temperature and have received substantial interest for energy conservation and thermal ...control purposes. The use of PCMs in the construction of constant temperature buildings can improve the comfortable environment and save more energy. However, the leakage of PCMs during phase change process limits the application of PCMs. In this paper, a series of PCMs microcapsules with controllable core numbers is synthesized with paraffin (37 ℃) as the core and cross-linked chitosan as the wall. The single-core phase-change microcapsules (S−PCM) and multicore phase-change microcapsules (M−PCM) were prepared by adjusting the preparation condition. The latent heat of S−PCM and M−PCM are 61.4 mJ mg−1 and 50.1 mJ mg−1, respectively. The S-PCM and M−PCM display good stability without paraffin leakage. In addition, the composite blocks of gypsum and S−PCM (GSCM) and M−PCM (GMCM) were prepared and the thermoregulatory effection was investigated, where the surface temperature of GSCM was 5–10 ℃ lower than that of pure gypsum block. PCMs may also have broad application space in electronics, cold chain, and other industries.
Four β-cyclodextrin/4,4′-diphenylmethane diisocyanate/polyethylene glycol (β-CD/MDI/PEG) crosslinking copolymers with different crosslinking density were prepared and characterized as novel polymeric ...solid–solid phase change materials (SSPCMs) for thermal energy storage. In the SSPCMs, PEG acts as the phase change functional chain and β-cyclodextrin (β-CD) acts as the molecular framework. The results from wide-angle X-ray diffraction (WAXD) and polarizing optical microscopy (POM) show that the synthesized SSPCMs have good crystallization properties and spherocrystal morphology with smaller size than that of PEG. According to the results of differential scanning calorimetry (DSC) and thermogravimetry (TG) curves, the SSPCMs possess high phase change enthalpies, good reusability, thermal reliability and stability. It is concluded that the crosslinking density of SSPCMs is a crucial factor significantly influenced the free movement and crystallization of PEG segments, and then affects phase transition properties of SSPCMs.
•Four crosslinking β-CD/MDI/PEG copolymers were synthesized as solid–solid PCMs.•The copolymers have spherocrystal morphology with smaller size than that of PEG.•The crosslinking density of the copolymers effects their phase change properties.•The copolymers have high phase change enthalpy and good thermal reliability.
•A mathematical model of the packed-bed TES with PCM capsules is established.•The PCM-TES is utilized in CSP system which is coupled with S-CO2 Brayton cycle.•Influence of melting temperature on ...performances of the cascaded PCM-TES is studied.•The thermal performances of the non-, two-, and three-cascaded PCM-TES systems are compared.•A design method for maximizing effective utilization rate of PCM is proposed.
In the concentrating solar power (CSP), the thermal energy storage system (TES) is under the constraint of the outlet threshold temperatures. Therefore optimizing the distribution of phase change materials (PCM) with different melting temperature is an effective way to improve the performance of PCM-TES. In the study, a mathematical model of the packed-bed TES system with PCM capsules is established, and the PCM-TES is under the constraint of the outlet threshold temperatures in charging and discharging processes. Based on the model, the effects of the melting temperature on the performances of the non-cascaded, two-cascaded, and three-cascaded PCM-TES are studied. The results are concluded as follows. (1) For the non-cascaded PCM-TES, the effective utilization rate of the PCM is greatly affected by the melting temperature. The maximum utilization rate is only about 40%. (2) For the two or three cascaded PCM-TES, the effective utilization rates of PCM can be greatly improved by choosing a reasonable melting temperature. (3) A design criterion of melting temperature is proposed with the goal of the maximum effective utilization rate for cascaded PCM-TES under the constraint of outlet threshold temperature in CSP. Using this proposed criterion, the effective utilization rate can reach 84%, which is about twice as high as that in non-cascaded PCM-TES. The results of optimizing the distribution of PCMs with different melting temperatures can be beneficial for the various application of the PCM-TES system which is under the constraint of outlet threshold temperature.
This paper studies the enhanced heat transfer of adding longitudinal fins in a horizontal shell-and-tube heat storage unit. A two-dimensional numerical model is established and validated through ...comparing with experimental data in literature. Under the same ratio of fin volume to phase change materials (PCMs), the melting thermal performance is optimized by changing the fin thickness, interval and the number. Results demonstrate that adding longitudinal fins is a simple and effective method to enhance the thermal energy storage efficiency. The number of fins greatly affects the complete melting time, and the maximum time difference caused by the number of fins is as high as 72.85% under the same phase change material (PCM) filling mass. At the same time, increasing the number of fins will weaken the local natural convection. In this paper, the optimal number of fins in the limited research range is given, and the effectiveness of longitudinal fins in improving melting speed is quantified, which has certain practical significance for the engineering application research of phase change energy storage.
•Optimal number of fins is given in a horizontal finned thermal energy storage unit.•Melting time can maximally be saved as high as 72.85% by increasing fin number.•Blindly increasing fin numbers cannot further improve the energy storage speed.•Heat conduction plays a leading role in paraffin melting process for a finned TES application.
•Insight investigation of passive phase-change materials.•The application of PCM in vehicle applications.•Discussion about the perks and disadvantages of PCM.•Numerical solution of a hybrid solution ...combining PCM and liquid cooling system.
In this paper, an extensive review of a battery thermal management systems (BTMSs) such as phase-change materials (PCMs) in the state of art is proposed. Nowadays, PCMs are particularly attractive and chosen as one of the most interesting cooling system in terms of high-energy storage density. In addition, they are less bulky, complex and expensive than traditional cooling methods such as forced-air cooling or liquid cooling. Nonetheless, the integration of PCMs in a battery application calls for an analysis that will enable the researcher to proposed optimized BTMSs. Indeed, due to the lack of literature in this domain, the paper proposed to review all the existing studies on battery applications involving PCMs. Numerical analysis description, heat transfer theory along with the classification of the existing components for PCMs are also presented. This paper is based on previous reviews to help to update the thin number of references, which is considered by the authors as the major contribution.
•A novel battery thermal management with flexible phase change material is proposed.•The assembly of proposed thermal management design is facile and technically simple.•The thermal contact heat ...transfer characteristic is investigated experimentally.•The thermal management performance is evaluated under different load profiles.
Traditional battery thermal management (BTM) with phase change material (PCM) is constrained by the problems of leakage, low thermal conductivity and high rigidity of PCM from the assembly perspective. Herein, we report an innovative and facile BTM with thermally induced flexible composite PCM (FCPCM). In this design, battery could be clinched to the FCPCM with an interference fit because of the thermally induced flexibility and shape recovery of FCPCM. Such an assembly is designed to be compact and efficient with no need for thermal grease. The steady-state measurement results show that different phase states of PCM have different thermal interface properties. The integration associated with the shape recovery of FCPCM could cause a low thermal contact resistance between battery and FCPCM. As a result, the constructed passive BTM exhibits an excellent thermal control performance. When the battery is discharged from 100% to 0% charge state, the maximum temperature of FCPCM based BTM is 43.4 °C during 2.5C discharge rate, which is 28.8 °C lower than No PCM. For the conditions of dynamic stress test and charge–discharge cycle, it shows lower temperature fluctuation within the acceptable range and the long-time function of latent heat of PCM could be recovered. With these prominent performances, the BTM performed here with respect to assembly methods and process flexibility will provide insights into the passive BTM system.
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