受限结晶与微观传热耦合作用下石蜡相变乳液过冷现象的机理研究

Phase change paraffin emulsion is a novel multi-functional fluid, which has the ability to store and transfer heat simultaneously. It has potential applications in various industries, such as the storage of solar energy and recovery of industrial waste heat. However, the application of phase change paraffin emulsion suffers from supercooling phenomenon, which reduces the ability of phase change paraffin emulsion to store and transfer heat remarkably. In order to diminish the supercooling phenomenon of phase change paraffin emulsion, a correlation between the supercooling degree of phase change paraffin emulsion and the diameter of paraffin particle as well as the cooling rate is derived theoretically in this proposal, which is from the point of view of convective heat transfer from micro particle to water and combined with the Gibbs – Thomson’s equation. The correlation shows that the supercooling degree of phase change paraffin emulsion does not increase monotonically with the decrease in diameter of paraffin particle. In the project presented, phase change paraffin emulsions with different particle size distributions will be prepared via mechanical agitation, sonication, and high-pressure homogenization with selected surfactant, co-surfactant, and electrolyte. The mechanism of supercooling of phase change paraffin emulsion, i.e. the dependence of supercooling degree on the diameter of paraffin particle and the cooling rate under coupled effect of confined crystallization and microscale heat transfer, will be interpreted based on experimental determinations of supercooling degree and particle size distribution of phase change paraffin emulsion. The results obtained will provide theoretical guidance for the preparation and application of phase change paraffin emulsion with low supercooling degree.

石蜡相变乳液是集储热与传热于一体的新型功能流体，在太阳能存储和工业余热回收等领域具有广阔的应用前景。但石蜡相变乳液在使用时会出现过冷现象，极大降低了其储热与传热的性能。为抑制石蜡相变乳液的过冷现象，本项目首先以流体中微粒子的对流传热过程为对象，结合吉布斯—汤姆森方程，推导出石蜡相变乳液的过冷度与石蜡粒子粒径和降温速率之间的理论关系式，预测了石蜡相变乳液的过冷度在石蜡粒子的粒径减小时非单调性变化的特征。在此基础上，项目拟筛选适宜的表面活性剂、助表面活性剂和电解质，采用机械搅拌、超声波破碎和高压均质等方法制备不同粒度的石蜡相变乳液，然后通过实验测量其过冷度和粒度，以揭示受限结晶与微观传热耦合作用下，石蜡相变乳液的过冷度随石蜡粒子粒径和降温速率的变化规律，为低过冷度石蜡相变乳液的制备和应用提供理论指导。

本项目以Span 80和Tween 80为复合乳化剂，正丁醇为助表面活性剂，采用相转变法制得了稳定的石蜡相变乳液，并对其性质进行了表征，研究了乳液组成和乳化工艺对石蜡相变乳液性质的影响。.提出了一种测量石蜡相变乳液过冷度的新方法，即平衡态比容法；利用该方法，准确测量了不同粒度的石蜡相变乳液的过冷度；在此基础上，对石蜡相变乳液过冷现象的微观机制进行了分析。.用氢氧化镁铝和氧化石墨烯的纳米颗粒代替化学乳化剂，采用高剪切乳化法，制备了一种低过冷度，低黏度，高度稳定，具有光热转换功能的新型石蜡Pickering乳液，并对其性质进行了表征，特别是储热和传热性能。实验结果表明，在所制备的石蜡Pickering乳液中，氢氧化镁铝和氧化石墨烯的纳米颗粒均匀分布在石蜡-水界面上。这些纳米颗粒作为外源晶核，引发石蜡异相成核结晶，从而从根本上解决了石蜡相变乳液的过冷问题。所制备的石蜡Pickering乳液具有优异的光热转换、传热和储热性能，在太阳能存储、工业余热回收和建筑物温度智能调控等领域具有广阔的应用前景。.