Abstract:

Cu nanoparticles were added into the deionized water with dispersant and ultrasonic wave to prepare the dispersive Cu-H₂O nano fluid. The effect of nano fluid on the characteristics of vacuum flash ice preparation by changing the particle size and the mass fraction of nano fluid under the 100 Pa was explored experimentally. As the results showed, adding nano particles into water without dispersant (nano particles have settling phenomenon), can reduce the supercooling degree of water, and shorten the time of phase change. However the uniform dispersion of nano fluid without settlement can significantly shorten the time of phase change, and the supercooling degree is reduced by 37%. At the initial flash moment, nano fluid has little effect on the cooling process of liquid phase. The larger the mass fraction of the nano fluid, the shorter the icing time, and the greater the cooling rate of the solid phase. The phase transformation time is shortened with the decrease of the particle size, but the temperature drop rate is almost the same in the solid phase. The change of particle size has little effect on the supercooling degree of the solution, which is basically maintained at 1.5℃ at lower concentration.

Key words: Cu nanoparticles, vacuum, ice production, supercooling degree, phrase change

摘要：

在去离子水中加入Cu纳米颗粒，通过添加分散剂和超声波振荡，配制均匀分散的Cu-H₂O纳米流体。在100 Pa初始压力下，通过改变纳米颗粒粒径、纳米流体质量分数研究均匀分散的纳米流体对真空闪蒸制冰实验特性的影响。结果表明，水中加入纳米颗粒（无分散剂，纳米颗粒有沉降现象），可降低水过冷度，缩短相变结冰时间，而分散均匀无沉降的纳米流体可显著缩短相变时间，使过冷度降低37%；在闪蒸瞬间，纳米流体对液相降温过程几乎没有影响；纳米流体质量分数越大，结冰时间越短，固相降温段降温速率越大；随着纳米颗粒粒径减小，相变时间缩短，而固相降温阶段温降速率几乎相同，较低浓度时（0.05%），粒径的改变，对纳米流体过冷度影响不大，基本维持在1.5℃。

关键词: Cu纳米粒子, 真空, 制冰, 过冷度, 相变