相变材料的过冷特性及调控研究进展

Supercooling Characteristics and Its Adjustment of Phase Change Material:a Review

相变材料(Phase change material,PCM)由于具有较大的潜热值、合适的相变温度及稳定的性质,在储热(冷)领域具有广阔的应用前景。但是,相变材料通常存在过冷现象,而过冷会降低相变材料的结晶温度,影响相变材料的储热性能和放热温度区间。在相变材料中添加成核剂是目前应用最为广泛的降低过冷度的方法。近年来,学者对成核剂的研究主要集中在针对不同的相变材料,筛选出高效、稳定性好且添加比例小的成核剂。此外,采用外加扰动的方式也可以降低相变材料的过冷度,如机械冲击、超声辐射或电场等,这一方法虽然出现较早,也同样具有良好的降低过冷度的效果,但因为需要额外的设备支持,所以目前的研究和应用较少。近年来,研究者通过改变相关参数,如选择合适的超声频率、电场强度等,来达到更好的降低相变材料过冷度的效果。微胶囊相变材料早期采用封装前添加成核剂的方式降低过冷度,但这会降低其储热能力,近年来的研究工作通过控制微胶囊尺寸和壁面改性这两种方式降低微胶囊的过冷度,它可以在不降低储热能力的情况下降低过冷度,因而具有较好的前景。本文介绍了相变材料的过冷特性,阐述了冷却速率、壁面效应、尺寸效应等因素对过冷特性的影响,分析了降低相变材料过冷度的方法。最后指出了相变材料过冷特性研究存在的问题,提出了在相变材料过冷度预测、过冷度影响因素的作用机理和改进降低过冷度方法上需进一步研究。

Phase change material(PCM)has a wide application prospect in the field of heat storage(cold)due to its large latent heat value,suitable phase transition temperature,and stable properties.However,phase-change materials usually have a phenomenon of supercooling,which affects the release of latent heat when the phase change material stores heat.The addition of nucleating agents to phase change materials is the mostcommonly used method to reduce the degree of supercooling,at pre-sent.In the past years,researchers in this field have focused on screening nucleating agents with higher efficiency,better stability and lower specific gravity for different phase change materials.In addition,the method of plus disturbance can similarly reduce the supercooling degree of phase change materials,such as mechanical shock,ultrasonic radiation or electric field,which appears earlier and reduced the degree of supercooling.Considering the requirement for additional equipment support,there are few researches and applications at present.Recently,it has been shown that selecting the relevant suitable parameters,such as ultrasonic frequency and electric field,can substantially enhance the supercooling effect of phase change materials.The microcapsule phase change material initially reduces the degree of supercooling by adding a nucleating agent before encapsulation,along with the side effect of weakening its heat storage capacity.Researchers began to concentrate on controlling the size of the microcapsule and optimizing the structure of the microcapsule shell in recent years,with a useful application prospect,which can decrease the degree of supercooling and maintain the heat storage capacity.Supercooling characteristics of phase change materialsare introduced in this paper firstly.Then,the effects of cooling rate,shell surface and ambient temperature on the supercooling characteristics are clarified in detail.Following,different methods about reducing the degree of supercooling are allowed analyzing the advantages and disadvantages.Finally,the problems existing in the study of supercooling characteristics of phase change materials are emphasized.It is suggested that further researches are needed in establish a supercooling prediction model,actors affecting supercooling and its mechanism and improved supercooling reduction method.