含圆柱状颗粒纳米流体的湍流流动和传热特性研究

The shape of particles has an important effect on the turbulent flow and heat transfer characteristics of nanofluids. However, most of the current researches are based on nanofluids containing spherical particles. Research shows that convective heat transfer enhancement of non-spherical particles based nanofluids is better than that of spherical particles based nanofluids. Since the shape of many kinds of non-spherical nanoparticles can be approximated by cylinders, this project focuses on water based nanofluid suspensions with cylindrical nanoparticles. The particle size and orientation distribution are obtained by method of moments and orthogonal closure technique, respectively. Numerical simulations are implemented the turbulent flow and convective heat transfer characteristics of nanofluids containing cylindrical particles in a circular tube. The flow loop experiments on cylindrical nanoparticles based two phase flow are carried out in order to obtain the friction factor and Nusselt number features along the path. The project aims at the following goals: (1) to reveal the cylindrical nanoparticle concentration distribution and orientation distribution in pipe flow; (2) to reveal the turbulent drag reducing features and convective heat transfer characteristics of nanofluid pipe flow with cylindrical nanoparticles. The above study provides theory and experimental analytical methods for the choice of particle shape and concentration of nanofluids for the application in the field of energy and chemical engineering.

颗粒形状对纳米流体湍流流动及传热特性有着重要的影响，目前的研究主要集中在含球状颗粒的纳米流体，而非球形纳米颗粒比球形纳米颗粒对流体的对流传热性能有着更为显著的影响。考虑到很多非球形纳米颗粒的形状可以由圆柱来近似，本项目拟以含圆柱状颗粒的水基纳米流体为研究对象，采用矩方法求解得到流场中的颗粒尺度分布，利用正交封闭技术求解得到圆柱状颗粒的取向分布，并通过数值模拟得到圆管中含圆柱状颗粒纳米流体的湍流流动及对流传热特性。同时，设计完成含圆柱状颗粒纳米流体在圆管中的对流传热实验，获得沿程的阻力系数及努塞尔数变化规律。最终完成如下目标：(1) 揭示圆管流动中圆柱状纳米颗粒的浓度分布和取向分布规律；(2) 揭示含圆柱状颗粒纳米流体圆管流动的湍流减阻规律及对流传热特性。本项目的研究为纳米流体在能源、化工等领域的应用中在颗粒形状、浓度等方面的选择提供必要的理论支撑和实验分析方法。

将纳米颗粒分散到液体中制成的纳米流体被认为是新一代的传热工质。研究表明，采用非球形颗粒制备的纳米流体有着更为优异的传热性能，尤其是圆柱状颗粒对纳米流体的强化传热效果最好，具有良好的应用前景。.本项目针对含圆柱状颗粒的水基纳米流体为研究对象，构建了纳米流体在圆管中作层流及湍流流动用于强化传热时，描述分散其中的圆柱状颗粒群浓度分布的一般动力学方程，以及描述圆柱状颗粒在不同流态下的取向分布方程；耦合圆柱状颗粒群平衡信息与圆管流动信息构建两相流动模型并求解，并与实验数据比较得出结论。.对于直管中的纳米流体流动，发现颗粒在壁面附近存在较大的浓度梯度，壁面效应使颗粒取向趋于流动方向；随机力使中心区的颗粒浓度均一，且主轴趋于随机取向。纳米流体的黏性随着颗粒体积分数的增加而变大，压降随流速线性增加，流动阻力随着圆柱状纳米颗粒长径比的增加而增加，充分发展的流动断面速度剖面会因柱状颗粒的存在而变得平坦，且随着长径比的增加更明显。纳米流体的对流传热系数大于基液的对流传热系数，并随着颗粒长径比的增加而增加。随着流速的增加，形状效应逐渐消失。在低流速区域，颗粒形状对传热的影响较为明显，综合考虑阻力损失和传热强化之比，含圆柱状颗粒纳米流体可应用于低功耗微型通道的冷却应用。对于弯管中的纳米流体的湍流流动，随机力导致颗粒数浓度均匀分布。随着斯托克数、迪恩数、雷诺数和颗粒长径比的增加，颗粒数浓度分布的不均匀程度增加。随着斯托克数和颗粒长径比的增加或是迪恩数和雷诺数的减少，更多颗粒的长轴与沿流动方向对齐。穿透率随着迪恩数、雷诺数和颗粒长径比的降低而增加。该研究有利于减少阻塞，避免故障和提高系统效率。.在本项目资助下，项目组在国内外高水平学术刊物和会议上共撰写和发表相关论文12篇，其中8篇被SCI收录，3篇被CSCD-C收录；参加国际学术会议5人次，国内学术会议2人次。