成核剂与增稠剂对甘露醇相变特性的影响

Effects of nucleating agents and thickening agents on phase change characteristics of D-mannitol

糖醇是一种用于储热的相变材料,具有较高的潜热,然而,糖醇的高过冷度阻碍了其应用。D-甘露醇作为一种糖醇,在中温储热方面具有广阔的应用前景。选用氧化铝和碳化硅作为成核剂,海藻酸钠和羧甲基纤维素作为增稠剂,观察了纯甘露醇、成核剂、增稠剂以及单独或联合添加成核剂和增稠剂的甘露醇的形貌。采用差示扫描量热法研究了成核剂和增稠剂对甘露醇相变特性的影响。实验结果表明,氧化铝、碳化硅和适量的海藻酸钠促进了甘露醇的成核结晶,当氧化铝、碳化硅、海藻酸钠的质量分数分别为7.0%、9.0%、0.5%时达到最低过冷度,样品相比纯甘露醇过冷度分别降低了17.4、12.2和17.3℃。联合添加相比单独添加成核剂和增稠剂改善了甘露醇的成核结晶;当联合添加氧化铝和海藻酸钠的质量分数分别为5.0%和1.0%,而碳化硅和海藻酸钠的质量分数分别为3.0%和1.0%时,样品相比纯甘露醇过冷度分别降低了19.7℃、16.5℃。探讨了成核剂和增稠剂对甘露醇相变特性的影响机理,发现增稠剂提高了成核剂在甘露醇样品中的分散性,因而提高了成核剂的诱导成核作用。

Sugar alcohols is a type of phase change materials with high latent heat for thermal energy storage.However,the supercooling degrees of sugar alcohols are high,which hinder their applications.D-mannitol,as a sugar alcohol,is promising for medium-temperature thermal energy storage.In this study,the effects of nucleating agents and thickening agents on the phase change characteristics of D-mannitol are studied by differential scanning calorimeter.Aluminum oxide and silicon carbide are selected as nucleating agents,while sodium alginate and carboxymethyl cellulose are selected as thickening agents.The morphologies of the pure D-mannitol,nucleating agents,thickening agents,and D-mannitol with individual or combined nucleating agents and thickening agent are observed.The results show that the nucleation and crystallization of D-mannitol are promoted by aluminum oxide,silicon carbide and sodium alginate of proper amounts.When the mass fraction of aluminum oxide,silicon carbide and sodium alginate is 7.0wt%,9.0wt%and 0.5wt%,the lowest supercooling degree is obtained,which is 17.4℃,12.2℃and 17.3℃,respectively lower than that of pure D-mannitol.The combination of nucleating agent and thickener improves the nucleation and crystallization of D-mannitol compared with the addition of individual nucleating agent or thickener.When the mass fraction of aluminum oxide and sodium alginate are 5.0wt%and 1.0wt%,respectively,the supercooling degree of the sample is reduced by 19.7℃compared with pure D-mannitol.When the mass fraction of silicon carbide and sodium alginate are 3.0wt%and 1.0wt%,respectively,the supercooling degree of the sample is reduced by 16.5℃compared with pure D-mannitol.The mechanism for the effects of the nucleating agents and thickening agents on the phase change characteristics of D-mannitol are discussed.It is found that the thickening agents enhance the dispersion of the nucleating agents in the D-mannitol samples,thus improving the nucleation induction effects of the nucleating agents.