氧化石墨烯纳米流体过冷度及非均匀成核条件研究

Supercooling Degree and Heterogeneous Nucleation Condition of Graphene Oxide Nanofluids

为研发过冷度低的相变蓄冷材料,降低冰蓄冷系统的能耗,实验测试了5种不同浓度的水基氧化石墨烯纳米流体的过冷度,并采用非均匀成核理论计算了在氧化石墨烯纳米薄片上的成核条件。实验结果表明,跟去离子水相比,各种浓度纳米流体的过冷度均受到了极大抑制,最大可降低69.1%,而且成核时间也大大缩短。理论计算表明:在单层氧化石墨烯纳米薄片的侧面(厚度)上成核需要很大的过冷度,只有当纳米薄片的重叠层数达到6层以上或重叠后的厚度超过6nm时,有效成核对应的过冷度才接近本实验条件下氧化石墨烯纳米流体的最大过冷度;要在纳米薄片的上下表面成核,过冷度与纳米薄片边长的乘积必须大于或等于2.446×10-8 m·K,借助纳米薄片的粒径分布和过冷度实验结果,验证了氧化石墨烯纳米流体满足这一成核条件。研究结果表明,氧化石墨烯纳米薄片可以作为降低相变材料过冷度的成核剂,对冰蓄冷和快速制冰行业具有重要的指导意义和实用价值。

To develop phase change materials（PCMs）with lower supercooling degree to reduce energy consumption in ice storage system,experiments were conducted to measure the supercooling degree of five nanofluids containing different mass fractions of graphene oxide,and the nucleation condition of nanofluids was evaluated following the theory of heterogeneous nucleation.The results indicate that the supercooling degree of nanofluids is greatly suppressed,and the supercooling degree can be reduced by 69.1%at most,furthermore the nucleation starts in advance.Theoretical calculation demonstrates that ice nucleus cannot grow on the thicknesssurfaces of the single graphene oxide nanosheet;only when the layers of graphene oxide nanosheet reach to more than six,the supercooling degree of effective nucleation approaches the greatest supercooling degree of the graphene oxide nanofluids under these connditions;when the nucleation occurs on the top or bottom surface,the product of the supercooling degree and thenanosheets size gets equal to or greater than 2.446×10-8 m·K,which is verified by the results of nanosheets size distribution and supercooling degree.It indicates that graphene oxide nanosheet can be used as a nucleating agent for reducing supercooling degree of PCMs in ice storage and rapid ice making.