【作者】 吴鹏；

【导师】 邱利民； 张学军；

【作者基本信息】 浙江大学 ， 制冷及低温工程， 2008， 硕士

【摘要】 冰蓄冷中央空调能够有效的实现“削峰填谷”,成为储能技术发展的主要方向之一。但由于水结冰时存在过冷度,使得能耗增大,如何减小过冷度是蓄冰技术研究的热点。本文首先介绍了动态制冰方式的概况,并在此基础上对成核的相关问题进行了实验研究和理论分析。在纯净水的结冰成核实验中,介绍了包括壁面粗糙度、冷却速率和壁面材料等因素对成核的影响。在对壁面成核机理进行了理论分析后,建立了液体在壁面的润湿性质(以接触角表示)与成核能力(以临界成核半径表示)之间的定量关系。通过向纯净水中添加纳米微粒成核剂,发现不同的纳米粒子具备的成核能力不同;添加活性剂、超声振荡等因素均会影响到粒子悬浮特性,进而影响到粒子的成核;此外,纳米粒子具备的强化传热特性在实验中也得到了体现。通过添加剂成核机理的分析,发现粒子的成核性能与其润湿性、晶格结构相联系,由此可得到蓄冰溶液成核添加剂的选择标准。针对间壁式换热器中的冰堵现象,本文分析了近壁面流体边界层的情况,包括近壁面流体温度场分布和热流密度变化,发现均匀的流体温度场会影响到蓄冰流体的制冰量及其在壁面的粘附,提出采用超疏水性涂层、均匀温度场和添加适量的抗冻物质相结合的方法来防止壁面冰层的粘附。更多还原

【Abstract】 Ice-making cold thermal energy storage systems have been in the spotlight because they act on flatting the electric power load curve in the daytime in summer, which has a peak due to the use of air-conditioning. Water is widely used as the phase change material for thermal storage because of such advantages as high latent heat of melting, stability, low cost and so on. However, there are a few disadvantages with the use of water. One of the most serious problems is the supercooling phenomenon that occurs in the process of solidifying water of the cold storage.The pure water had been used as the basic fluid. Some factors, such as the roughness of the vessel, the cooling rate, the material of the vessel had been studied. Besides, the nucleation mechanism of the vessel surface based on the relationship between the characteristic of the surface and the critical nuclation radius had been obtained.According to adding nanoparticles to pure water, the decreasing of supercooling degree had been observed. The dispersants and ultrasonic vibration would affect the stable and eveness of the nanoparticle, giving a further affection on the nucleation. The heat transfer enhancement of the nanofluids had also been studied.Based on the study above, the charactristics of the nanoparticles aiming at decrease the supercooling degree of the water had been acquired, which lie on the wettability and the crystal structure between the basic fluid and the addition.This paper had also studied the temperature boundary layer of the fluid near the inner suface of the vessel, including the heat flux of the fluid. Some methods had been studied to avoid the adhesion in the surface type heat exchanger. The results in this paper will make a good foundation for rebuilding the dynamic ice making system.更多还原