变物性纳米流体传热传质机理研究

发布时间：2018-05-27 06:46

本文选题：纳米流体 + 变物性参数　；参考：《大连海事大学》2016年硕士论文

【摘要】：纳米流体是指把金属或非金属纳米粉体分散到水、醇、油等传统换热介质中,制备成均匀、稳定、高导热的新型换热介质,这是纳米技术应用于热能工程这一传统领域的创新性研究。本文分别对纳米流体自然对流传热与纳米流体强迫对流的传热机理进行了研究。在处理偏微分守恒方程组时,本文采用了一种新的相似方法,不仅使方程组的求解更加简便,二维速度场的研究更加直观,还使变物性参数的研究更为方便。本文取得的主要成果如下：(1)本文基于Buongiorno的模型,在合理的假设条件下建立了平板纳米流体自然对流与强迫对流的模型。并分别考虑了常物性与变物性两种情况。(2)应用新方法对模型简化并求解。结果显示：对于纳米流体自然对流传热,提高主流温度会使速度及温度升高,并使速度的最大值位置远离平板。当考虑变物性参数时,壁面温度升高会使速度增大且最大值处靠近平板,同时会使温度降低。对于纳米流体强迫对流传热,物性参数作为常数处理时,速度值与普朗特数的变化无关,温度梯度会随普朗特数的升高而明显增大。当考虑变物性参数时,主流温度升高会使速度梯度以及温度梯度减小,壁面温度升高则会使速度梯度以及温度梯度增大。(3)对计算结果进行函数拟合,得到纳米流体对流换热的传热量以及平均努赛尔数的计算公式以及强迫对流的表面摩擦系数的计算公式。纳米流体在强化传热领域具有广阔的应用前景,对于提高热交换系统的经济性、可靠性和小型化具有重要意义。在众多传热方式中,对流传热无论在生活中还是生产中都较为常见。对纳米流体在边界层中的对流现象进行理论研究对实际生产具有一定指导作用。
[Abstract]:Nanometer fluid is a new type of heat transfer medium, which is prepared by dispersing metal or nonmetallic nanometer powder into traditional heat transfer media such as water, alcohol, oil and so on, which is uniform, stable and highly conductive. This is an innovative study on the application of nanotechnology in the traditional field of thermal engineering. In this paper, the heat transfer mechanism of natural convection and forced convection of nanoscale fluids are studied. In dealing with partial differential conservation equations, a new similarity method is used in this paper, which not only makes the solution of equations more convenient, the study of two-dimensional velocity field is more intuitive, but also makes the study of variable physical parameters more convenient. The main results obtained in this paper are as follows: (1) based on Buongiorno's model, a model of natural convection and forced convection of plate nanoscale fluids is established under reasonable assumptions. The new method is applied to simplify and solve the model. The results show that for the natural convection heat transfer of nanoscale fluids, increasing the mainstream temperature will increase the velocity and temperature, and make the position of the maximum velocity far away from the plate. When variable physical parameters are taken into account, the increase of wall temperature will increase the velocity and the maximum value will be near the plate, and the temperature will decrease at the same time. For forced convection heat transfer of nanoscale fluids, when the physical parameters are treated as constants, the velocity value is independent of the change of Plantt number, and the temperature gradient will obviously increase with the increase of Plantt number. When variable physical parameters are considered, the velocity gradient and temperature gradient will decrease when the mainstream temperature is raised, and the velocity gradient and temperature gradient will increase with the increase of wall temperature. The formulas of heat transfer, average Nussel number and surface friction coefficient of forced convection are obtained. Nano-fluid has a broad application prospect in the field of heat transfer enhancement, and it is of great significance to improve the economy, reliability and miniaturization of heat exchange system. Convective heat transfer is common both in life and in production among many heat transfer modes. The theoretical study on the convection phenomenon of nanoscale fluid in the boundary layer is helpful to practical production.
【学位授予单位】：大连海事大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：TK124

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