Abstract: The current study explained the mechanism of heat transfer enhancement of nanofluids from the micro-flow aspect. The Eulerian-Eulerian and Euler-Lagrange multiphase models are implemented respectively to explore the flow field of nanofluids inside a horizontal circular tube under turbulent state.The pressure loss is used to validate the accuracy of predictions for each model, which is the most important flow parameter in turbulent flow but also is frequently ignored in previous numerical work.The results indicated that there is obvious velocity slip phenomenon between water and nanoparticles.Compared with the pure water, the development of nanofluids boundary layer is inevitably disturbed, which consequently decreases its thickness and thermal resistance.The distribution of nanoparticles in the entire flow field is not uniform, which improves overall heat transfer capacity inside the boundary layer. The present authors suggest the enhanced heat transfer capability of nanofluids is the result of altered flow characteristics when nanoparticles are present and the flow conditions are most important drivers of heat transfer enhancement in nanofluids. The thorough understanding on flow characteristics of nanofluids is essential for nanofluids flow, which is the basis of further utilization of nanofluids in engineering applications.

Key words: nanofluids, pressure drop, two-phase flow, turbulent flow, CFD

摘要： 采用Eulerian-Eulerian模型和Eulerian-Lagrange模型研究了TiO₂-水纳米流体在水平管内的湍流流动特性，并与实验结果进行对比分析，探讨了不同模型中各种相间作用力的影响。从微流动角度探索纳米流体的流动本质，从而进一步揭示其传热强化机理。结果表明：在壁面附近，纳米颗粒与水存在着明显的速度差异，相间的动量交换十分明显，从而强化了局部微流动，导致边界层变薄。纳米颗粒在整个流场内部是不均匀分布的，使得边界层内部换热能力得到大幅度增强。纳米流体流动特性的改变是影响其强化换热的主要因素。

关键词: 纳米流体, 压差, 两相流, 湍流, 计算流体力学