水基ZnO纳米流体电导和热导性能研究

Investigation on the thermal and electrical conductivity of water based zinc oxide nanofluids

利用水热法生成了形状规则、粒径均匀的球形ZnO纳米颗粒,并超声分散于水中,制备得到稳定的水基ZnO纳米流体.实验测量水基ZnO纳米流体在体积分数和温度变化时的电导率,并测试室温下水基ZnO纳米流体在不同体积分数下的热导率.实验结果表明,ZnO纳米颗粒的添加较大地提高了基液(纯水)的热导率和电导率,水基ZnO纳米流体的电导率随纳米颗粒体积分数增加呈非线性增加关系,而电导率随温度变化呈现出拟线性关系;纳米流体的热导率与纳米颗粒体积分数增加呈近似线性增加关系.本文在经典Maxwell热导模型和布朗动力学理论的基础上,同时考虑了吸附层、团聚体和布朗运动等因素对热导率的影响,提出了热导率修正模型.将修正模型预测值与实验值对比,结果表明修正模型可以较为准确地计算出纳米流体的热导率.

Spherical ZnO nanoparticles each with a uniform size are synthesized by a hydrothermal method. These ZnO nanoparticles are then dispersed into water by ultrasonic vibrating to form stable nanofluids. The electrical conductivity of water-based ZnO nanofluids with a variety of temperature and volumetric fractions are investigated. The volumetric-fraction-dependent thermal conductivity is also measured at room temperature. Experiments indicate that the electrical conductivity of ZnO nanofluid reveals a non-linear relationship versus volumetric fraction. However, it presents a quasi linear relationship versus temperature. The thermal conductivity is enhanced nearly linearly with volumetric fraction increasing. Moreover, a modified model is established based on Maxwell thermal conductivity model and Brownian dynamics theory by considering boundary adsorption layer, aggregation and Brownian motion of nanoparticles in the fluid. The expected thermal conductivity values based on the modified model are in good agreement with our experimental data, suggesting that our modified model might be more accurately adapted to the nanofluids thermal conductivity.