水基纳米流体的凝固行为

Solidification behaviors of water-based nanofluids

选用二氧化钛(TiO2)纳米颗粒、碳纳米管(CNT)和石墨烯(graphene)纳米片制备水基纳米流体。采用步冷曲线法测量纳米流体的凝固温度和时间。研究纳米材料形状、尺寸、接触角和比表面积对纳米流体凝固行为的影响。实验发现,TiO2纳米颗粒、CNT纳米管和石墨烯纳米片对纳米流体过冷度和凝固时间的减小作用依次增强。0.034%(质量分数)浓度的石墨烯纳米片可完全消除水的过冷现象,使其凝固起始时间和总时间分别缩短61.22%和30.53%。成核理论分析表明,纳米流体的凝固过冷度主要取决于单位体积纳米流体的成核面积。与接触角、形状和尺寸相比,纳米材料的比表面积对纳米流体过冷度的影响更大。

Titanium dioxide （TiO2 ）nanoparticles,carbon nanotubes （CNT）and graphene nanoplates were chosen to prepare water-based nanofluids.The solidification processes of graphene/water,CNT/water and TiO2/water nanofluids were measured by the cooling curve method.Effects of nanomaterial shape,size,contact angle and specific surface area on the supercooling degree,starting time and total time of solidification of water were investigated.It was found that graphene nanoplates and TiO2 nanoparticles had the strongest and weakest effects on decreasing the supercooling degree and solidification times of water,respectively.Graphene nanoplates of 0.034wt% eliminated the supercooling phenomenon of water completely,and reduced the starting time and total time by 61.22% and 30.53%,respectively.Analysis of nucleation revealed that the supercooling degree of nanofluid was mainly dependent on the total surface area of nanomaterials exposed to water.Compared to the contact angle,shape and size of nanomaterials,the specific area of nanomaterials was more important to the supercooling degree of nanofluid.