Abstract:

In order to improve the low thermal conductivity performance of carbonate molten salt, it is proposed to dope metal magnesium powder with ternary carbonate molten salt (Li₂CO₃-Na₂CO₃-K₂CO₃) to strengthen the thermal conductivity. The static melting method was used to prepare the composite carbonate salts with 1%(mass) or 2%(mass) magnesium powder. The morphology, structure, liquid density, specific heat capacity, and thermal diffusivity were characterized by the scanning electron microscope-energy dispersive X-ray spectrometer (SEM-EDX), Archimedes method, the differential scanning calorimeter (DIN specific heat measure standard) and the laser flash method, respectively. The thermal conductivity was finally calculated based on the density, specific heat capacity, and thermal diffusivity. The results showed that the introducing of magnesium powder changed the morphology of pure eutectic (ternary carbonate salt), a large number of spherical particles (2-5 μm) were detected in the composite salts. Comparison with the pure eutectic, the liquid density, thermal diffusivity and thermal conductivity of salt compound doped magnesium powder were enhanced, and the liquid specific heat capacity was diminished. The mean thermal conductivity of salt compound doped with 1% or 2% magnesium powder was enhanced by 21.67% and 19.07%, respectively. So, the 1% salt composite should be the promising HTF due to the enhancement of density, thermal diffusivity and thermal conductivity.

Key words: solar energy, carbonate salt, composites, magnesium powder, preparation, thermal conductivity, liquid

摘要：

为克服碳酸熔盐热导率较低的不足，提出通过向三元碳酸熔盐（Li₂CO₃-Na₂CO₃-K₂CO₃）掺杂金属镁粉来改善导热性能的新思路，采用静态熔融法制备了掺杂1%、2%掺镁碳酸熔盐复合材料。采用扫描电镜-X射线能谱、阿基米德法、差示扫描量热法（DIN比热测试标准）和激光闪光法，分别观察了掺镁碳酸熔盐形貌结构，测量了熔盐和复合熔盐液体的密度、比热容、热扩散系数，最后计算获得复合熔盐液体的热导率。研究结果表明，镁粉的加入改变了纯盐（三元碳酸熔盐）的形貌结构，熔体内形成大量的2~5 μm球体颗粒，与纯盐相比，1%掺镁碳酸熔盐液体密度、热扩散系数和热导率都得到增强，液体比热容减小，复合熔盐液体的平均热导率增加了21.67%；2%掺镁碳酸熔盐液体密度、热扩散系数和热导率同样得到增强，虽然复合熔盐液体的比热容减小，但其平均热导率仍然增加了19.07%。1%掺镁碳酸熔盐具有更高的液体密度、热扩散系数和热导率，可作为传热介质在太阳能热发电传蓄热系统推广。

关键词: 太阳能, 碳酸熔盐, 复合材料, 镁粉, 制备, 热导率, 液体