Supercooling of the microencapsulated phase change materials（PCMs） during cooling usually happens. This phenomenon can interfere with heat transfer and is necessary to further overcome. In this study, mela- mine-for...Supercooling of the microencapsulated phase change materials（PCMs） during cooling usually happens. This phenomenon can interfere with heat transfer and is necessary to further overcome. In this study, mela- mine-formaldehyde microcapsules containing two n-alkane PCMs, namely, n-dodecane（Cl2） or n-tetradecane（C14） were prepared by in situ polymerization. A small amount of n-hexatriacontane（C36） was introduced as an organic ge- lator into the core of microcapsules to cope with the supercooling problem. Analyses demonstrate that supercooling of the microencapsulated C12 or C14 was significantly suppressed by adding 3%（mass fraction） C36, without changing the spherical morphology and dispersibility. It could be also found that the enthalpy of microencapsulated CI2 or C14 containing C36 was similar to that of microencapsulated n-alkanes without C36, whereas the difference between onsets of crystallization and melting（degree of supercooling） is similar to that of those of pure n-alkanes, suggesting the re- markable suppression ability of the organic gelator on supercooling.展开更多
The objective of this paper is to investigate water supercooling. Supercooling occurs when a liquid does not freeze although its temperature is below its freezing point. In general, supercooling is an unstable conditi...The objective of this paper is to investigate water supercooling. Supercooling occurs when a liquid does not freeze although its temperature is below its freezing point. In general, supercooling is an unstable condition and occurs under special conditions. The parameters that influence supercooling stability and probability of occurrence include freezer temperature and water’s initial temperature. In this paper, it is shown that with a freezer temperature range of -3℃ to -8℃, supercooling is most likely to happen and is independent of the water’s initial temperature. Furthermore, as the freezer temperature decreases, the probability of nucleation increases, causing instant freezing. Finally, it is concluded that the Mpemba effect, in which initially hot water freezes faster than initially cold water, is due to the supercooling instability in initially hot water in which nucleation agents are more active.展开更多
Antarcticite, a mineral with composition CaCl2·6H2O and structure P321, is an ideal phase change material (PCM) due to the high energy storage density and good thermal conductivity. However, the existence of supe...Antarcticite, a mineral with composition CaCl2·6H2O and structure P321, is an ideal phase change material (PCM) due to the high energy storage density and good thermal conductivity. However, the existence of supercooling and incongruent melting would weaken its thermal properties and then hinder its application. In this paper, based on the cooling curve method and DSC measurement, we experimentally selected the minor SrCl2·6H2O as the nucleator and carboxyl methyl cellulose as the thickening agent, which could significantly reduce supercooling and partly restrain the incongruent melting. Moreover, we incorporated Antarcticite as PCM into building envelopes in four different cases, the simulation of the heat transfer processes showed that the temperature fluctuation could be reduced to about 2℃ in the best case.展开更多
The Li-ion battery is widely used in power tools, energy storage systems, and electric vehicles. In reality, battery thermal management is essential to control the battery temperature within a specific temperature ran...The Li-ion battery is widely used in power tools, energy storage systems, and electric vehicles. In reality, battery thermal management is essential to control the battery temperature within a specific temperature range. Although research has shown that preheating the battery at low temperatures on cold days can improve output performance significantly, few efforts have been made to study the preheating method in-depth. As a result, this research proposes two preheating designs for cylindrical batteries with supercooled phase change materials: Single-and dual-phase change material(PCM) designs. A mathematical model is developed to analyze the effect of the PCM layer’s height, thickness, and mass on the preheating effect for seven candidate PCMs with high supercooling degrees. Furthermore, the economic efficiency of the single-PCM design with different PCMs is compared. In addition, the optimal ratio of the PCMs’ height for the dual-PCM design is investigated. Eventually, the improvement of the battery’s output performance is discussed. The results reveal that the proposed designs can effectively preheat the battery with a temperature rise higher than 10°C. The single-PCM design using Li NO3·3H2O shows the best preheating ability, while CH3COONa·3H2O is the most economical. Although the dual-PCM design cannot outperform the single-PCM design, it can preheat the battery twice and show better flexibility. Compared with the battery without preheating, a 26650-format battery with the single-PCM design can prolong the operating time by 38.8 min and save the electric quantity by 2.1 A h;while they are by 42.8 min and 2.3 A h with the dual-PCM design.展开更多
Thermal energy storage(TES)using phase change materials(PCMs)is a powerful solution to the improvement of energy efficiency.The application of Ammonium alum(A-alum,NH4Al(SO_(4))_(2)·12H_(2)O)in the latent thermal...Thermal energy storage(TES)using phase change materials(PCMs)is a powerful solution to the improvement of energy efficiency.The application of Ammonium alum(A-alum,NH4Al(SO_(4))_(2)·12H_(2)O)in the latent thermal energy storage(LTES)systems is hampered due to its high supercooling and low thermal conductivity.In this work,modified A-alum(M-PCM)containing different nucleating agents was prepared and further adsorbed in expanded graphite(EG)to obtain composite phase change material(CPCM)to overcome the disadvantages of A-alum.Thermal properties,thermal cycle stability,microstructure and chemical compatibility of CPCM were characterized by differential scanning calorimetry,thermal constant analysis,scanning electron microscopy,X-ray diffraction and Fourier transform infrared spectroscopy.The cold rewarming phenomenon of CPCM was established and explained.Results showed that the latent heat and melting point of CPCM were 187.22 J/g and 91.54℃,respectively.The supercooling of CPCM decreased by 9.61℃,and thermal conductivity increased by 27 times compared with pure A-alum.Heat storage and release tests indicated that 2 wt%calcium chloride dihydrate(CCD,CaCl_(2)·2H_(2)O)was the optimum nucleating agent for A-alum.The result of TG and 30 thermal cycles revealed that CPCM exhibited favorable thermal stability and reliability during the operating temperature.The prepared modified A-alum/EG CPCM has a promising application prospect for LTES.展开更多
As a kind of essential hydrated salt phase change energy storage materials,mirabilite with high energy storage density and mild phase-transition temperature has excellent application potential in the problems of solar...As a kind of essential hydrated salt phase change energy storage materials,mirabilite with high energy storage density and mild phase-transition temperature has excellent application potential in the problems of solar time and space mismatch.However,there are some disadvantages such as supercooling,substantial phase stratification and leakage problem,limiting its further applications.In this work,for the preparation of shaped mirabilite phase change materials(MPcMs),graphene(GO),sodium carboxymethyl cellulose(CMC),and carbon nanofibers(CNFs)were used as starting materials to prepare lightweight CMC/rGO/CNFs carbon aerogel(CGCA)as support with stable shape,high specific surface area,and well-arranged hierarchically porous structure.The results show that CGCA has regular layered plentiful pores and stable foam structure,and the pore and sheet interspersed structure in CGCA stabilizes PcMs via capillary force and surface tension.The hydrophilic aerogels supported MPCMs decrease mirabilite leaking and reduce supercooling to around 0.7-1C.The latent heats of melting and crystallization of CGCA-supported mirabilite phase change materials(CGCA-PCMs)are 157.1 and 114.8 J-g-1,respectively.Furthermore,after 1500 solid-liquid cycles,there is no leakage,and the retention rate of crystallization latent heat is 45.32%,exhibiting remarkable thermal cycling stability.展开更多
以三水醋酸钠(CH3COONa.3H2O)为相变储热基材,添加各种不同成核剂和增稠剂,比较它们的效果,寻求储热性能优越的组合配方。实验表明:对于同一成核剂,随添加量的增加,CH3COONa.3H2O的过冷度有增大的倾向。在10 g CH3COONa.3H2O中添加0.05 ...以三水醋酸钠(CH3COONa.3H2O)为相变储热基材,添加各种不同成核剂和增稠剂,比较它们的效果,寻求储热性能优越的组合配方。实验表明:对于同一成核剂,随添加量的增加,CH3COONa.3H2O的过冷度有增大的倾向。在10 g CH3COONa.3H2O中添加0.05 g的Na2HPO4.12H2O,抑制过冷的效果最好,同时配合0.3 g羧甲基纤维素(CMC)使用,CH3COONa.3H2O的过冷性能得到进一步改善,过冷度可降低至2.015℃,并且还能有效地防止相分层。同时,还发现CH3COONa.3H2O体系的恒温温度为65℃比较合适。展开更多
文摘Supercooling of the microencapsulated phase change materials（PCMs） during cooling usually happens. This phenomenon can interfere with heat transfer and is necessary to further overcome. In this study, mela- mine-formaldehyde microcapsules containing two n-alkane PCMs, namely, n-dodecane（Cl2） or n-tetradecane（C14） were prepared by in situ polymerization. A small amount of n-hexatriacontane（C36） was introduced as an organic ge- lator into the core of microcapsules to cope with the supercooling problem. Analyses demonstrate that supercooling of the microencapsulated C12 or C14 was significantly suppressed by adding 3%（mass fraction） C36, without changing the spherical morphology and dispersibility. It could be also found that the enthalpy of microencapsulated CI2 or C14 containing C36 was similar to that of microencapsulated n-alkanes without C36, whereas the difference between onsets of crystallization and melting（degree of supercooling） is similar to that of those of pure n-alkanes, suggesting the re- markable suppression ability of the organic gelator on supercooling.
文摘The objective of this paper is to investigate water supercooling. Supercooling occurs when a liquid does not freeze although its temperature is below its freezing point. In general, supercooling is an unstable condition and occurs under special conditions. The parameters that influence supercooling stability and probability of occurrence include freezer temperature and water’s initial temperature. In this paper, it is shown that with a freezer temperature range of -3℃ to -8℃, supercooling is most likely to happen and is independent of the water’s initial temperature. Furthermore, as the freezer temperature decreases, the probability of nucleation increases, causing instant freezing. Finally, it is concluded that the Mpemba effect, in which initially hot water freezes faster than initially cold water, is due to the supercooling instability in initially hot water in which nucleation agents are more active.
文摘Antarcticite, a mineral with composition CaCl2·6H2O and structure P321, is an ideal phase change material (PCM) due to the high energy storage density and good thermal conductivity. However, the existence of supercooling and incongruent melting would weaken its thermal properties and then hinder its application. In this paper, based on the cooling curve method and DSC measurement, we experimentally selected the minor SrCl2·6H2O as the nucleator and carboxyl methyl cellulose as the thickening agent, which could significantly reduce supercooling and partly restrain the incongruent melting. Moreover, we incorporated Antarcticite as PCM into building envelopes in four different cases, the simulation of the heat transfer processes showed that the temperature fluctuation could be reduced to about 2℃ in the best case.
基金supported by the National Natural Science Foundation of China (Grant Nos. 51821004, 51876061)the Interdisciplinary Innovation Program of North China Electric Power University。
文摘The Li-ion battery is widely used in power tools, energy storage systems, and electric vehicles. In reality, battery thermal management is essential to control the battery temperature within a specific temperature range. Although research has shown that preheating the battery at low temperatures on cold days can improve output performance significantly, few efforts have been made to study the preheating method in-depth. As a result, this research proposes two preheating designs for cylindrical batteries with supercooled phase change materials: Single-and dual-phase change material(PCM) designs. A mathematical model is developed to analyze the effect of the PCM layer’s height, thickness, and mass on the preheating effect for seven candidate PCMs with high supercooling degrees. Furthermore, the economic efficiency of the single-PCM design with different PCMs is compared. In addition, the optimal ratio of the PCMs’ height for the dual-PCM design is investigated. Eventually, the improvement of the battery’s output performance is discussed. The results reveal that the proposed designs can effectively preheat the battery with a temperature rise higher than 10°C. The single-PCM design using Li NO3·3H2O shows the best preheating ability, while CH3COONa·3H2O is the most economical. Although the dual-PCM design cannot outperform the single-PCM design, it can preheat the battery twice and show better flexibility. Compared with the battery without preheating, a 26650-format battery with the single-PCM design can prolong the operating time by 38.8 min and save the electric quantity by 2.1 A h;while they are by 42.8 min and 2.3 A h with the dual-PCM design.
基金supported by the National key research and development plan of China(No.2022YFC3800401)the Fundamental Research Funds for the Central Universities(FRF-BD-20-09A).
文摘Thermal energy storage(TES)using phase change materials(PCMs)is a powerful solution to the improvement of energy efficiency.The application of Ammonium alum(A-alum,NH4Al(SO_(4))_(2)·12H_(2)O)in the latent thermal energy storage(LTES)systems is hampered due to its high supercooling and low thermal conductivity.In this work,modified A-alum(M-PCM)containing different nucleating agents was prepared and further adsorbed in expanded graphite(EG)to obtain composite phase change material(CPCM)to overcome the disadvantages of A-alum.Thermal properties,thermal cycle stability,microstructure and chemical compatibility of CPCM were characterized by differential scanning calorimetry,thermal constant analysis,scanning electron microscopy,X-ray diffraction and Fourier transform infrared spectroscopy.The cold rewarming phenomenon of CPCM was established and explained.Results showed that the latent heat and melting point of CPCM were 187.22 J/g and 91.54℃,respectively.The supercooling of CPCM decreased by 9.61℃,and thermal conductivity increased by 27 times compared with pure A-alum.Heat storage and release tests indicated that 2 wt%calcium chloride dihydrate(CCD,CaCl_(2)·2H_(2)O)was the optimum nucleating agent for A-alum.The result of TG and 30 thermal cycles revealed that CPCM exhibited favorable thermal stability and reliability during the operating temperature.The prepared modified A-alum/EG CPCM has a promising application prospect for LTES.
基金the financial supports from the Natural Science Foundation of Qinghai Province(Grant Nos.2020-ZJ-909 and 2021-ZJ-906)the Qinghai Thousand Talents Program(Grant No.724112)the Opening Project of State Key Laboratory of the New Technologies for Material Composites,Wuhan University of Technology(Grant No.2020-KF-1).
文摘As a kind of essential hydrated salt phase change energy storage materials,mirabilite with high energy storage density and mild phase-transition temperature has excellent application potential in the problems of solar time and space mismatch.However,there are some disadvantages such as supercooling,substantial phase stratification and leakage problem,limiting its further applications.In this work,for the preparation of shaped mirabilite phase change materials(MPcMs),graphene(GO),sodium carboxymethyl cellulose(CMC),and carbon nanofibers(CNFs)were used as starting materials to prepare lightweight CMC/rGO/CNFs carbon aerogel(CGCA)as support with stable shape,high specific surface area,and well-arranged hierarchically porous structure.The results show that CGCA has regular layered plentiful pores and stable foam structure,and the pore and sheet interspersed structure in CGCA stabilizes PcMs via capillary force and surface tension.The hydrophilic aerogels supported MPCMs decrease mirabilite leaking and reduce supercooling to around 0.7-1C.The latent heats of melting and crystallization of CGCA-supported mirabilite phase change materials(CGCA-PCMs)are 157.1 and 114.8 J-g-1,respectively.Furthermore,after 1500 solid-liquid cycles,there is no leakage,and the retention rate of crystallization latent heat is 45.32%,exhibiting remarkable thermal cycling stability.
文摘以三水醋酸钠(CH3COONa.3H2O)为相变储热基材,添加各种不同成核剂和增稠剂,比较它们的效果,寻求储热性能优越的组合配方。实验表明:对于同一成核剂,随添加量的增加,CH3COONa.3H2O的过冷度有增大的倾向。在10 g CH3COONa.3H2O中添加0.05 g的Na2HPO4.12H2O,抑制过冷的效果最好,同时配合0.3 g羧甲基纤维素(CMC)使用,CH3COONa.3H2O的过冷性能得到进一步改善,过冷度可降低至2.015℃,并且还能有效地防止相分层。同时,还发现CH3COONa.3H2O体系的恒温温度为65℃比较合适。
