Abstract:

The present work utilizes Molecular Dynamics (MD) method to simulate the micro-movements of nanoparticles in nanofluids. A simulation model of Cu nanoparticle in H₂O base fluid is established with MD method,which contains 26421 simulating particles. The diameter of the spherical nanoparticle is 4 nm. H₂O is modeled to be the base fluid because it is closer to the real situation of nanofluids,and it is easier to examine the influence of temperature on micro-movements of nanoparticles. It is found that the nanoparticles' movements is in high speed and random in directions. The rotational velocities of nanoparticles is in the range of 1×10⁹-1×10¹⁰ rad·s^-1; and the translational velocities of nanoparticles is in the range of 1-10 m·s^-1. When applying different temperatures,the velocity and temperature distributions of nanofluids are found to be different from single-phase base fluid. The main difference of nanofluids and base fluids is located at the near wall region. Both the velocity gradient and temperature gradient are larger than those of single-phase base fluid. The main reason for the different velocity distributions between nanofluids and base fluid is the random micro-motions of nanoparticles. Furthermore,the changed velocity characteristics influence the heat transfer process,which makes the temperature distribution of nanofluids is different from that of base fluid. Moreover,the temperature distribution of nanofluids changes a lot with the simulation,which can also distributed to the random micro-movements of nanoparticles in base fluid.

Key words: nanoparticles, molecular simulation, heat transfer, two-phase flow, transport

摘要：

建立了以水分子为基础液、以铜纳米颗粒为悬浮粒子的纳米流体模型，利用分子动力学模拟方法对纳米颗粒的微运动行为进行分析。研究发现纳米颗粒在基础液中具有高速的随机旋转与平移运动，旋转运动的角速度为1×10⁹~1×10¹⁰ rad·s^-1，平移运动的速度为1~10 m·s^-1。纳米流体速度分布与温度分布主要区别于单相基础液的位置在近壁面附近，纳米流体无论是速度梯度还是温度梯度均比单相流体的情况大，其主要原因是纳米颗粒在基础液中的随机运动，而改变的流体速度特性又会进一步影响传热过程。

关键词: 纳米粒子, 分子模拟, 传热, 两相流, 传递