Ji Jingwei,Li Wenju,Zhang Hongxiang,Zheng Yuechuan,Zhang Tengpu,Du Jinghui,Zhang Hong,Shi Bangkai
At present, research on dry powder for magnesium fire extinguishing is mostly focused on extinguishing surface fires, with limited research on internal smoldering. Moreover, fire extinguishing performance tests of dry powder are primarily conducted on horizontal surfaces, while inclined and vertical combustion poses greater hazards and extinguishing challenges. To address this issue, a new dry powder extinguishing agent (NaCl/PMHS@LMG) with a dual phase-change temperature range was prepared in this paper to extinguish surface open flames and internal smoldering generated by magnesium fires on non-horizontal surfaces. The extinguishing agent was made using sodium chloride (NaCl) and polymethylhydrosiloxane (PMHS)-modified low melting point glass powder (LMG). The results of material testing showed that the NaCl/PMHS@LMG exhibited a dual phase transition, featuring a lower initial phase transition temperature, greater thermal stability, and enhanced heat absorption. At the same time, the modification of PMHS converted LMG from hydrophilic to hydrophobic, enhancing the dry powder’s overall moisture resistance. The results of magnesium fire extinguishing experiments show that NaCl/PMHS@LMG can effectively extinguish magnesium fires in both stacked and vertical forms. Compared with NaCl, the average extinguishing time and consumption of NaCl/PMHS@LMG in stacked fires were reduced by 49% and 52.7%, respectively, and the temperature reduction rate of stacked surfaces during extinguishing was approximately 4 times faster than with NaCl. Additionally, NaCl/PMHS@LMG formed a three-layer air-isolated cover on the stack surface after extinguishing, with an “auto-filling” function that effectively extinguished internal smoldering in magnesium chip stacks. Subsequently, the extinguishing mechanism of the dry powder was further explored.
Passive thermal regulation materials are gaining increasing attention for their sustainability; however, conventional ones are usually limited to a single temperature condition, failing to meet the varying temperature demands across different seasons. To address this challenge, inspired by penguins’ thermoregulatory strategies, this study develops a composite phase change material that enables distinct regulation mechanisms under varying conditions. This material features a Janus surface that can switch between photothermal absorption and radiative cooling to cope with cold daytimes and hot environments; two distinct phase change ranges can maintain temperature balance on comfortable nights and achieve long-term thermal compensation on cold nights. Outdoor tests demonstrated that the material achieves 9.0℃ daytime cooling and extends nighttime comfort duration by 27.3% in hot weather, while in cold weather it averages 11℃ daytime warming and keeps nighttime temperature 0.5℃ above ambient; simulation results further showed that roof application of this material can effectively improve thermal comfort in diverse regions throughout the year. This work integrates photothermal absorption, radiative cooling, and dual-phase change processes, providing a feasible strategy for enhancing all-season thermal comfort in building energy conservation.
In this study, a kind of novel double phase change energy storage materials (DPCESM) based on two kinds of phase change nanocapsules and bentonite was reported. The nanocapsules ( n -ODE@CLPS and n -ESE@CLPS) were synthesized with n -octadecane ( n -ODE) and n -eicosane ( n -ESE) as phase change material (PCM), respectively, crosslinked polystyrene (CLPS) as shell, and DNS-86 as polymerizable emulsifier via soap-free miniemulsion polymerization method . The morphology, thermal energy storage capacity, and structure of nanocapsules and DPCESM were characterized and analyzed, respectively. Besides, the effects of DNS-86 on the thermal storage performance of nanocapsules were investigated. The results showed that the encapsulation efficiency of nanocapsules was the highest along with the excellent chemical stability and heat storage capacity when the percentage of polymerizable emulsifier was 2 wt%. The average diameter of n -ODE@CLPS was 136 nm, and the latent heat of phase change and encapsulation efficiency were 140.39 J/g and 91.28%, respectively. Meanwhile, the average diameter of n -ESE@CLPS was 134 nm, the latent heat of phase change and encapsulation efficiency were 148.32 J/g and 91.77%, respectively. Besides, the melting points of DPCESM were 26.25 °C and 34.58 °C, and the heat storage capacity was 90.17 J/g. Moreover, because of the doping of bentonite, the thermal conductivity of DPCESM can reach to 0.45 W/(m·K), which is 104.5% and 150% larger than pure n -ODE and n -ESE, respectively. The DPCESM can be used to adjust the indoor temperature and would be widely used as a promising composite phase change material.
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