Supercooling of phase change materials (PCMs) during solidification is a major problem in cold thermal energy storage (CTES), which reduces energy efficiency and aggravates energy waste. This study focuses on the supercooling characteristics of PCMs under heterogeneous nucleation, which provides a new idea for researching the influence of different dispersants on the supercooling degree of aqueous solution. The optimal ratios of CNTs water dispersant (TNWDIS) and polymer polyacrylic acid sodium (PAAS) to multi-walled carbon nanotubes (MWCNTs) in mannitol aqueous solution are determined through microstructure and cooling characteristics. How these two surfactants and MWCNTs with different concentrations and particle sizes influence the supercooling degree of nanofluids are investigated. The results indicate that the effect of PAAS is greater than that of TNWDIS. Furthermore, under the action of two dispersants and particle sizes of MWCNTs, the fitting equations of supercooling changing with the concentration of MWCNTs are obtained. In the light of the heterogeneous nucleation theory, with the enlargement of the particle size and the diminution of the contact angle affected by the dispersants, the interfacial free energy of heterogeneous nucleation of PCMs on the surface of nanoparticles is reduced. The supercooling degree therefore decreases. Specifically, the nucleation mechanism is deduced and analyzed through the contact angle and nucleation free energy formula.

中文翻译：

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多相成核下甘露醇相变体系的过冷特性

凝固过程中相变材料 (PCM) 的过冷是冷热储能 (CTES) 中的一个主要问题，这会降低能源效率并加剧能源浪费。本研究着眼于多相成核作用下PCMs的过冷特性，为研究不同分散剂对水溶液过冷度的影响提供了新的思路。通过微观结构和冷却特性确定了碳纳米管水分散剂 (TNWDIS) 和聚合物聚丙烯酸钠 (PAAS) 与多壁碳纳米管 (MWCNTs) 在甘露醇水溶液中的最佳比例。研究了这两种表面活性剂和不同浓度和粒径的多壁碳纳米管如何影响纳米流体的过冷度。结果表明PAAS的效果大于TNWDIS的效果。此外，在两种分散剂和多壁碳纳米管粒径的作用下，得到了过冷随多壁碳纳米管浓度变化的拟合方程。根据异相成核理论，随着分散剂作用下粒径的增大和接触角的减小，相变材料在纳米颗粒表面异相成核的界面自由能降低。因此过冷度降低。具体地，通过接触角和成核自由能公式推导和分析成核机制。得到了过冷度随多壁碳纳米管浓度变化的拟合方程。根据异相成核理论，随着分散剂作用下粒径的增大和接触角的减小，相变材料在纳米颗粒表面异相成核的界面自由能降低。因此过冷度降低。具体地，通过接触角和成核自由能公式推导和分析成核机制。得到了过冷度随多壁碳纳米管浓度变化的拟合方程。根据异相成核理论，随着分散剂作用下粒径的增大和接触角的减小，相变材料在纳米颗粒表面异相成核的界面自由能降低。因此过冷度降低。具体地，通过接触角和成核自由能公式推导和分析成核机制。因此过冷度降低。具体地，通过接触角和成核自由能公式推导和分析成核机制。因此过冷度降低。具体地，通过接触角和成核自由能公式推导和分析成核机制。