Leonard J P, Chung S J, Nettleship I, Soong Y, Martello D V, Chyu M K
Department of Mechanical Engineering and Materials Science, University of Pittsburgh, 848 Benedum Hall, Pittsburgh, PA 15261, USA.
J Nanosci Nanotechnol. 2008 Dec;8(12):6361-6.
Aqueous zinc oxide (ZnO) suspensions were prepared using a two-step preparation method in which an aggregated nanocrystalline ZnO powder was dispersed in water using a polyelectrolyte. The fluid showed anomalously high thermal conductivity when compared with the Maxwell and Hamilton-Crosser predictions. However, analysis of the particle size distribution showed that the fluid contained aggregated 20 nm crystallites of ZnO with a high volume fraction of particles larger than 100 nm. Sedimentation experiments revealed that particles settled out of the stationary fluid over times ranging from 0.1 hours to well over 10,000 hours. The size of the particles remaining in suspension agreed well with predictions made using Stoke's law, suggesting flocculation was not occurring in the fluids. Finally, a new concept of nanofluid stability is introduced based on the height of the fluid, sedimentation, Brownian motion and the kinetic energy of the particles.
采用两步制备法制备了水性氧化锌（ZnO）悬浮液，其中使用聚电解质将聚集的纳米晶ZnO粉末分散在水中。与麦克斯韦和汉密尔顿-克罗斯预测相比，该流体显示出异常高的热导率。然而，粒度分布分析表明，该流体包含聚集的20nm ZnO微晶，其中大于100nm的颗粒体积分数很高。沉降实验表明，颗粒在0.1小时到超过10000小时的时间内从静止流体中沉降出来。悬浮液中剩余颗粒的尺寸与使用斯托克斯定律做出的预测非常吻合，这表明流体中没有发生絮凝。最后，基于流体高度、沉降、布朗运动和颗粒动能引入了纳米流体稳定性的新概念。
