Abstract:

Different drying patterns of modified SiO₂ nanofluid droplets have been observed and the effects of modified SiO₂ nanoparticle deposition layer formed in boiling on pure water boiling heat transfer have also been investigated experimentally. The different drying patterns of nanofluid droplets show that modified function groups can affect whether SiO₂ nanoparticles can be adsorbed to the liquid-air interface, and based on this result a conjecture has been made about the effects of modified functional groups on the way of nanoparticle deposition during boiling of nanofluids. From boiling experiments, it is found that polyethylene glycol (PEG) groups modified SiO₂ nanoparticles deposition layer on a heater surface can increase average roughness of the heater surface a lot from 160 nm to 977 nm, and it can also increase pure water boiling heat transfer coefficient. However, the sulfonic acid groups modified SiO₂ nanoparticles deposition layer on a heater surface affect average roughness of the heater surface a little (increased 60 nm), and it deteriorates the pure water boiling heat transfer coefficient. The effects of modified functional groups on the deposition of nanoparticles during the boiling process inferred by droplet evaporation experiments were verified by boiling heat transfer experiments.

Key words: silica, nanoparticles, evaporation, deposition, boiling heat transfer

摘要：

实验研究了改性SiO₂纳米流体液滴蒸发后的沉积图案，以及改性SiO₂纳米颗粒沸腾沉积层对沸腾换热的影响。液滴蒸发实验研究表明：改性官能团会影响改性SiO₂纳米颗粒是否吸附在液-气界面，从而推断出在沸腾过程中改性官能团对纳米颗粒沉积方式的影响。沸腾实验研究结果表明：用聚乙二醇基团改性的SiO₂纳米颗粒沸腾沉积层使加热面的平均粗糙度从160 nm大幅增长到977 nm，且能增强纯水的沸腾传热系数；而用磺酸基团改性的SiO₂纳米颗粒沸腾沉积层对加热面的平均粗糙度的改变不明显，只使其增大了60 nm，且恶化了纯水的沸腾传热系数。通过沸腾换热实验结果较好地验证了通过液滴蒸发实验推断出的沸腾过程中改性官能团对纳米颗粒沉积方式的影响。

关键词: 二氧化硅, 纳米粒子, 蒸发, 沉积物, 沸腾换热