磁激励下近换热面区域磁性纳米粒子流动及传热机理研究

Either nano-fluid or magnetic fluid technology has drawbacks in the further enhancement of heat transfer performance. However, there are rare researches on strengthening heat transfer mechanism for magnetic nanofluids. Based on the advantages of the nano-fluid and magnetic fluid technologies, this paper constructs a magnetic nanofluid enhanced heat transfer system with magnetic excitation, and studies the flow and strengthening heat transfer mechanism of the near heat transfer surface area. This system solves the contradiction between magnetic variable thermal conductivity and the increase of viscosity coefficient. The proposed studies are as follows: The modified potential energy function and molecular potential energy model will be established by molecular dynamics theory. And the micromechanism of polymerization, arranging of magnetic nanoparticles under the magnetic excitation will be stuied. This paper will construct the kinematic relation of magnetic nanoparticles under unidirectional and alternating magnetic field, and the boundary layer theoretical equation of near wall surface will be established. The rheological model of the magneto-magnetic nanofluid in the magnetic excitation will be derived, and its characteristic flow characteristics will be studied. This paper will reveal the heat conduction and convective heat transfer mechanism in the near heat transfer surface area under the magnetic field. This paper will study the strengthening heat transfer performance under different magnetic field intensities and directions, different volume fraction, different heat transfer surface structures and different initial and boundary conditions by using the method combining the theoretical research and experimental researches. The system has better application prospect in heat transfer of electronic products, microchannel, high efficiency heat exchanger and air conditioner.

纳米流体和磁流体技术，在进一步提高传热性能上存在瓶颈；而针对于磁性纳米流体强化传热的机理研究不足。本课题结合二者优势，构建磁激励下磁性纳米流体强化传热系统并研究其近换热面区域的流动、传热机理。该系统解决了增强磁场强度在提高磁流体导热系数的同时也增加了粘滞系数的矛盾，拟展开如下研究：通过分子动力学理论建立修正势能函数和分子势能模型，研究磁激励下磁性纳米粒子的聚合、排列微观机理；构建单向及交变磁场下磁性纳米颗粒的运动关系，并建立近壁面处的边界层理论方程；推导磁纳米流体在磁激励时的流变模型，研究其特有的流动特性；揭示磁场下近换热面区域的导热和对流换热机理；利用理论与实验结合的方法研究不同磁场强度和方向、磁性纳米颗粒体积分数、换热面结构及不同初始和边界条件下的强化传热性能，并以此为依据实现换热的主动控制及优化运行。该系统在电子产品、微通道、高效能换热器、空调两器的强化传热中有较好的应用前景。

纳米流体和磁流体技术，在进一步提高传热性能上存在瓶颈；而针对于磁性纳米流体强化传热的机理研究不足。磁纳米流体在电子产品、微通道、高效能换热器、空调两器的强化传热中有较好的应用前景。. 通过分子动力学理论建立修正势能函数和分子势能模型，研究磁激励下磁性纳米粒子的聚合、排列微观机理。构建单向及交变磁场下磁性纳米颗粒的运动关系，并建立近壁面处的边界层理论方程。推导磁纳米流体在磁激励时的流变模型，研究其特有的流动特性。揭示磁场下近换热面区域的导热和对流换热机理。. 研究表明，增大磁纳米流体的质量分数可以强化对流换热。磁激励下，与流动方向平行的磁场会恶化磁纳米流体的传热性能。垂直的磁场会使对流换热性能增强，增加的幅度与磁场强度和雷诺数成正比。垂直方向交变磁场的激励使磁纳米流体的对流换热性能进一步提高，增强的幅度与磁场强度成正比，与交变频率和雷诺数成反比。. 利用理论与实验结合的方法研究不同磁场强度和方向、磁性纳米颗粒体积分数、换热面结构及不同初始和边界条件下的强化传热性能，并以此为依据实现换热的主动控制及优化运行。