【作者】 张洋念；

【导师】 虞维平；

【作者基本信息】 东南大学 ， 热能工程， 2005， 硕士

【摘要】 长期以来,霜层内部结构的准确描述和热物性的精确确定,一直是对结霜机理研究的一个难题。因此,本文首先针对结霜初期的生长结构问题,研制出了一套可以观测霜层生长过程图像的结霜实验装置,通过对结霜条件的控制,为分析结霜过程的特性提供实验依据,并且该设备还解决了国内很多结霜实验图片拍摄不清晰和倍数较小的问题,可以拍摄到较大倍率的清晰的图像。在搭建了实验平台的基础上,本文对结霜初期的生长变化规律进行了大量了实验研究,取得了很多有用的实验数据,并对各种实验现象给予了分析和讨论。本文在对霜层生长特性充分的认识之后,结合了现有一维随机成核生长模型,考虑了冷表面温度和环境温度对霜层生长的影响,建立了霜层一维生长模型,运用计算机图像处理技术,将模拟出来的图像和实验中拍摄到的图像进行对比,得到比较一致的结果。再运用分形理论,对模拟生长图片进行分形维数的计算,发现模拟图像具有分形特征且随着霜层厚度的增加,分形维数随之增大。为了能对霜层内部的导热过程有个比较清晰、直观的了解,本文运用有限差分法,对霜层剖面进行了离散化处理,以能量守恒原理为基础,列出了网格点的控制离散方程组。结合霜层固有的不均匀特性,综合考虑各网格界面上复杂的导热系数的处理和选取,运用线性方程组的求解方法,获得各点温度值。使用数学工具软件Matlab编程,求得各种霜层模型的导热系数。本为将分形渗流结构引入到霜层结构的描述中,建立了霜层生长初期滞回生长阶段的结构模型,运用以上建立的导热模型,求得霜层导热系数随密度变化的曲线,并与其他常用模型求得的曲线进行比较,结果表明本文建立的霜层模型的导热系数与结霜初期实际的导热系数变化规律更加吻合,在一定范围内有其合理性。更多还原

【Abstract】 Describing the inner structure and the thermal properties of frost layer is a very important and difficult project. So, a frosting experiment equipment which can observe the process of initial stages of frosting is firstly designed. Compared with many other frosting experiment equipments, it can give us a very big and clear image of frosting.Base on the experiment equipment, a series of experiments are done for the initial frosting process and many experiment datum are gotten. According to those datum, many discusses and analysis are done for those different kind of frosting phenomenon.With fully understanding of frosting successive growth character, combined with one-dimensional successive nucleation growth model and considering the influence of temperature on cold layer and in atmosphere, a computer simulation model of frosting growth is presented. To compare the simulating image with the real image by use of the computer, coherent result can be gotten. A series of patterns and their fractal dimensions are obtained for different conditions. With the increase of frost layer, the fractal dimensions are increasing either.In order to understand the conduction in the frost, by using finite difference method on a control volume, the frost section is discretized. Combined with the energy equation, the discretization equations are deduced. Owing to the inherent asymmetric property of the frost, the conductivity of the interfaces are processed and selected. The temperature distributions are counted finally. Then, the efficient conductivity is counted with considering the influence of the density and the void rate by using Matlab.Fractal infiltration construction are used to describe the inner construction of initial frosting. The curve which can describe the conductivity change with the density are built. compared with the old model, it has its rationality.更多还原