低体积分数水基SiO2纳米流体沸腾换热关键物性参数研究

Study on critical characteristics of boiling phase change of dilute SO2-water nanofluids

中文关键词: 二氧化硅  纳米颗粒  纳米流体  制备  热物性

英文关键词: silica  nanoparticles  nanofluids  preparation  thermophysical properties

中文摘要:

      在不添加任何分散剂和改变PH值的情况下，通过两步法将比表面积为150 m2/g的气相SiO2纳米颗粒制备成均匀稳定、透明度高、分散性能好的纳米流体。并对该功能性纳米流体进行了导热系数、黏度、表面张力和壁面接触角的测量。低体积分数下，功能性纳米流体较基液的导热系数几乎没有变化，但粘度却有较大改变。传统固液两相混合物黏度模型不再适用功能性纳米流体的计算，其主要原因是传统公式低估了分子间作用力对纳米流体黏度的影响。因此，建立了功能性纳米流体的黏度经验公式。由于纳米颗粒的存在提高了沸腾表面的粗糙度，从而使纳米流体的壁面湿润性能大大提高。实验结果表明，纳米流体的黏性和壁面接触角是沸腾换热发生骤变的关键。

英文摘要:

      Functional nanofluids are prepared by two-step process. It is can be prepared without any dispersant and the change of pH value. Functional nanofluids refer to SiO2-water nanofluids with a specific surface area of 150 m2/g and silica nanoparticles prepared by CVD. The nanofluid have uniform, stability, high transparency and good dispersion performance. And the thermal conductivity, viscosity, surface tension and solid-liquid contact angle of the functional nanofluids were also measured. At low concentration, nanoparticles in the fluid has little effect on thermal conductivity, but viscosity are greatly changed. The traditional solid-liquid two-phase mixture viscosity model is no longer suitable for the calculation of functional nanofluids. The main reason is that traditional formulas underestimate the influence of intermolecular forces on the viscosity of nanofluids. Therefore, the empirical formula for the viscosity of functional nanofluids is established. Compared to the pure water, the nanofluid can significantly increase the wettability of the wall surface is that the nanoparticles increases the roughness of the heated surface. Thereby, it is greatly improving the wettability of the nanofluid. The experimental results show that viscosity and wall contact angle of nanofluids are the key to sudden changes in boiling heat transfer.