热传导论文：杂质对热传递影响的理论模拟.doc

热传导论文：杂质对热传递影响的理论模拟【中文摘要】热电效应,也称温差电效应,是一种可以实现热能和电能之间相互转换的效应,可用于温差发电或热电制冷。相对于传统的发电和制冷方式,利用热电效应进行发电和制冷具有可靠性高,无污染等优点。热电效应包括Seebeck效应,Peltier效应和Thomson效应。热电材料的应用非常广泛,不仅可用于温差发电,家电制冷,医疗器材等方面,并有望利用汽车尾气进行废热发电。热电材料的性能一般由无量纲的优值系数zT值表示,zT值越高,材料的热电转换效率越高。ZT=S2/,其中S、分别为Seebeck系数、电导率和热导率。目前制约热电材料大规模应用的主要原因就是过低的ZT值,所以提高热电材料的ZT值就成了热门研究方向。而提高热电材料ZT值的主要方法之一就是通过调节材料组分来降低材料的热导率。一般情况下,常温发电的实际应用要求ZT值大于等于1。在制冷方面,要想达到氟利昂压缩制冷机的效率,要求材料的ZT值要大于等于3。随着计算机技术的发展,计算机模拟已经成了除了理论和实验以外,对材料物理性质研究的重要手段,分子动力学模拟就是基于对小粒子的模拟来计算物质的宏观特性的学科。本论文为了研究在不同掺杂情况下,固体材料热传导所受到的影响,通过自编程序,分别对一维简单原子链和二维晶格模型进行了可视化的模拟。模拟过程利用牛顿第二定律和分子动力学中的Verlet算法,建立格点之间的运动方程。分别在体系内掺入不同性质的杂质,给定体系的一端一个初始位移,从而产生晶格振动,在此初始条件的基础上求解粒子的运动方程,通过记录声子传播到末端粒子时的能量与初始能量的比值来判断杂质对热传导的影响。通过上述研究,本论文取得的主要创新之处如下：一、通过自编程序,可视化的模拟了一维简单原子链和二维原子链在受到扰动下的振动情况。模拟结果显示,晶格的振动要在两个端面之间来回多次散射,最终把能量分散在整个晶格中。到达末端的第一个能量峰值为其携带的最大能量值,能量经过几次反射以后逐次降低。模拟结果还显示任何不同于基体元素的杂质都会对热传导产生一定程度的影响。二、以一维简单原子链为模型,通过设置循环程序,分别模拟了在一维体系内掺入不同质量比、弹性系数比、分散度的杂质,计算得到了不同性质杂质阻碍体系内能量传递的规律。三、以二维原子链为模型,通过设置循环程序,在相同体系内掺入不同质量比、弹性系数比、分散度的杂质,模拟计算得到了杂质阻碍体系内能量传递的规律。本论文分别以一维和二维晶格为模型,通过自编程序,可视化的模拟了能量在晶格内部的传递。研究结果表明,若在体系内掺入相同数量的杂质,且杂质具有相同的弹性系数比,质量比取一组变化值,一维和二维的情况得到了相同的结果,即杂质的质量与基体材料原子质量越相近,越不利于降低材料的热导率。若在体系内掺入相同数量的杂质,且杂质具有相同的质量比,弹性系数比取一组变化值,杂质的弹性系数相对于基体材料原子的弹性系数越小,越有利于降低材料的热导率。当相同性质和数量的杂质分别以不同的分散度掺入相同的体系内以后,模拟发现杂质放置的越分散,将越有利于阻碍晶格的能量传递。【英文摘要】Thermoelectric effect is an achievable energy conversion effect between thermal energy and electric energy, which can be used for thermoelectric power generation or thermoelectric cooling. Thermoelectric power generation and cooling technology are pollution-free and very reliable and so on. Traditionally, the term thermoelectric effect encompasses three separately identified effects:the Seebeck effect, the Peltier effect, and the Thomson effect. The application of thermoelectric materials is very extensive, not only can be used for thermoelectric power generation, refrigeration appliances, medical equipment, etc, but also can be expected to use vehicle exhaust for cogeneration. The dimensionless figure of merit ZT represents the performance of thermoelectric materials. And higher ZT values will make higher efficiency of the thermoelectric conversion. ZT=SS2/k, where S、and k, are Seebeck coefficient, electrical conductivity and thermal conductivity, respectively. Currently, the low ZT values of available materials restrict the applications of this technology with large scales. Much research in thermoelectric materials has focused on increasing the ZT. One of the main methods to improve the ZT of thermoelectric materials is to reduce the thermal conductivity by adjusting the component. Today for power generation devices that operate near room temperature have a ZT of about 1. The thermoelectric material designed to replace a conventional Freon-gas refrigerator must have a ZT of equal to or larger than 3. With the development of computer technology, computer simulation has become one of the most important means to research the physical properties of materials. Molecular dynamics simulation is based on a small particle simulation to calculate the macroscopic properties.In order to investigate how the different doping methods, this thesis separately simulates a simple one-dimensional atomic chain model and two-dimensional atomic chain model through the programming. The simulation sets up the equations of motion between the grid points by using Newtons second law and the Verlet algorithm of molecular dynamics. If different impurities are doped into the system, giving an initial displacement to one end of the system, and then the lattice begins to vibrate. The other end of the system will have the end energy through the phonon transmission, by calculating the ratio of the end energy and the initial energy to determine the impact of the impurities on the thermal conduction. Through these researches mentioned above, this thesis has achieved the following major innovations:1. This thesis separately simulates a simple one-dimensional atomic chain model and two-dimensional atomic chain models vibration through the programming, when two kinds of atomic chain are disturbed. Simulation results show that the lattice vibration will go through multiple scattering between both ends and eventually spread the energy throughout the crystal. The first energy peak which reaches the end is the maximum end energy. And the end energy will reduce after a few reflections. The results also show that any impurities will affect the thermal conduction.2. Through the programming, this thesis separately simulates the conditions that different of quantities, mass and elasticity coefficient of impurities are doped into one-dimensional atomic chain system, and get the law of obstructing energy transfer by impurities.3. Through the programming, this thesis separately simulates the conditions that different of quantities, mass and elasticity coefficient of impurities are doped into two-dimensional atomic chain system, and get the law of obstructing energy transfer by impurities.This thesis use programming to simulate the influence of impurities on thermal conductivity. The results show that:Doped within the system with the same quantity and the elasticity coefficient ratio of impurities, the mass ratio takes a set of values, both one-dimensional model and two-dimensional model will get the same result. The more similar of the mass of impurity atoms and the mass of the substrate materials, the less help to reduce the thermal conductivity. Doped within the system with the same quantity and the mass ratio of impurities, the elasticity coefficient ratio takes a set of values. The smaller of the elasticity of impurity atoms compared with the elasticity of the substrate materials, the more help to reduce the thermal conduction. Doped within the system with the same quantity and property of impurities, the more dispers