利用SiO_2纳米颗粒增强硝酸盐储热材料比热容的实验研究

Enhancement of specific heat capacity of nitrate salts using SiO_2 nanoparticles

多元混合硝酸盐作为高温传热流体在聚光式太阳能热发电系统中具有良好的应用前景。本工作利用水溶液法,在具有较低熔点的NaNO_3-KNO3-LiNO_3三元共混合硝酸盐中掺入SiO_2纳米颗粒,有效地提高了混合硝酸盐储热材料的比热容,其中掺入较低质量分数(0.0625%)的纳米颗粒比掺入较高质量分数(1%、0.25%)的纳米颗粒能获得更高的比热容。利用聚乙烯吡咯烷酮(polyvinylpyrrolidone,PVP)作为分散剂,增强了Si O2纳米颗粒在硝酸盐中的分散性,有效地缓解了制备过程中纳米流体中纳米颗粒的团聚。同时,本工作还研究了纳米颗粒的团聚对其增强比热容效果的影响,并通过使用分散剂,进一步提高了硝酸盐储热材料的比热容。最终结合上述关系,引入界面热阻和半固体层模型,讨论了掺入纳米颗粒增强硝酸盐储热材料比热容的机理。

As high temperature heat transfer fluids, hybrid nitrate salts play a promising role in application of concentrating solar thermal power system. In this study, the heat capacity of NaNO3-KNO3-LiNO3 ternary hybrid nitrate heat storage materials were effectively enhanced by doping SiO2 nanoparticles with aqueous solution method. With comparison of different mass ratio of nanoparticles, we found that lower mass ratio of nanoparticles has more effective enhancement on heat capacity. The effect of agglomeration of nanoparticles on heat capacity enhancement was also studied. By using polyvinylpyrrolidone（PVP）, we reduced the agglomeration of nanoparticles and the dispersity of nanoparticles in nitrate salts was improved which showed furtherly enhancement of heat capacity of nitrate salt heat storage materials. Combined with the results above, we introduced the interface thermal resistance and semi-solid layer model, and the mechanism of heat capacity enhancement of nitrate salt materials by doping nanoparticles was discussed.