二氧化硅纳米颗粒对液滴冻结特性的影响

Effect of silicon dioxide nanoparticles on freezing characteristics of droplets

为了改善液滴的冻结特性,以含SiO2纳米颗粒的液滴为研究对象,研究了不同SiO2纳米颗粒含量(5 mg/mL、10 mg/mL、30 mg/mL、50 mg/mL)和不同冷表面温度(268 K、265 K、263 K)对液滴动态冻结特性(液滴形变、接触角、冻结时间等)的影响。结果表明:二氧化硅液滴(SiO_(2)-H_(2)O)的冻结时间受过冷度和SiO_(2)纳米颗粒含量的影响。在低过冷度(263K)时,10 mg/mLSiO_(2)-H_(2)O加速冻结,可加快34.78%,在高过冷度(265 K和263 K)时,5 mg/mLSiO_(2)-H_(2)O均表现为延迟冻结,分别延缓21.2%和36.84%。此外,根据液滴形变特性,SiO_(2)纳米颗粒可以使初始液滴砂化加剧,减少冻结液滴内部气泡的释放。SiO_(2)纳米颗粒与固液相界面之间相互影响,使得液滴冻结完成时纵向变化率减少,横向形变增强,液滴在外形轮廓上变得更加圆润。

To enhance the freezing properties of droplets,droplet containing silica nanoparti-cles were used,the impact of varying concentrations of SiO_(2) nanoparticles(5 mg/mL,10 mg/mL,30 mg/mL,50 mg/mL)and different cold surface temperatures(268 K,265 K,263 K)on droplet freezing characteristic(droplet deformation,contact angle,and freezing time)was investigated.The results showed that the freezing time of silica droplets(SiO_(2)-H_(2)O)is affected by the degree of su-percooling and the content of SiO_(2) nanoparticles.At low supercooling temperature(263 K),10 mg/mL SiO_(2)-H_(2)O accelerates freezing by 34.78%,but at high supercooling temperature(265 K and 263 K),5 mg/mL SiO_(2)-H_(2)O shows delayed freezing by 21.2% and 36.84%,respectively.In addition,SiO_(2) nanoparticles can intensify the opacification of the initial droplets and reduce the release of bubbles inside the frozen droplets according to the deformation characteristics of the droplets.The interaction between SiO_(2) nanoparticles and the solid-liquid phase interface cause the longitudinal change rate to be reduced,and the transverse deformation to be enhanced.The drop-lets are more rounded in profile when freezing was completed.