热传导论文杂质对热传递影响的理论模拟讲解

1、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二S2(r/ k ,其中S、八k分别为Seebeck系数、电导率和 热导率。目前制约热电材料

2、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

3、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

4、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

5、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 electricenergy,which can be used for thermoelectric power

6、 gen erati on or thermoelectric cooli ng. Thermoelectric power gen erati on and cooli ng tech no logy are polluti on-freeand very reliable and soon. Traditi on ally,the term thermoelectric effect en compassesthree separately ide ntified effects:the Seebeck effect, the Peltier effect, and the Thoms o

7、n effect. The applicati on of thermoelectric materials is very exte nsive, not only can be used for thermoelectric power generation, refrigeration applia nces, medical equipme nt, etc, but also can be expected to use vehicle exhaust for coge nerati on. The dime nsionl ess figure of merit ZT represen

8、ts the performanee of thermoelectric materials. And higher ZT values will make higher efficiency of the thermoelectric conversion. ZT=SS2(T /k, where S 、 (T and k,are Seebeck coefficient, electrical conductivity and thermal conductivity, respectively. Currently, the low ZT values of available materi

9、als restrict the applications of this tech no logy 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 con ductivity by adjust ing the comp onent.Today for power

10、gen eratio n devices that operate n ear 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 tha n 3. With the developme nt of computer tech no logy, computer simulatio n has become one of th

11、e most importa nt means to research the physical properties of materials. Molecular dynamics simulation is based on a small particle simulation to calculate the macroscopic propertiesn order to inv estigate how the differe nt dop ing methods, this thesis separately simulates a simple on e-dime nsion

12、al atomic chain model and two-dimensional atomic chain model through the programming. The simulation sets up the equations of motion betwee n the grid points by using Newt on s sec ond law and theVerlet algorithm of molecular dyn amics. If differe nt impurities are doped into the system, giving an i

13、nitial 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 theratio of the end energy and the initialenergy to determine theimpact of the impurities on the thermal conductio

14、n. Through these researches mentioned above, this thesis has achieved the following major innovations:1. This thesis separatelysimulates a simple one-dimensional atomic chain model and two-dimensional atomic chain model s vibration through theprogram ming, whe n two kinds of atomic cha in are distur

15、bed.Simulation results show that the lattice vibration will go through multiple scatteri ng betwee n both ends and eve ntually spread the energy throughout the crystal. The firstenergy peakwhich reaches the end is the maximum end en ergy. And the end en ergy will reduce after a few reflecti ons. The

16、 results also show that any impurities will affect the thermal conduction.2. Through the program ming, this thesis separately simulates the con diti ons that differe nt of qua ntities, mass and elasticity coefficie nt of impurities are doped into on e-dime nsional atomic cha in system, and get the l

17、aw of obstruct ing en ergy transfer by impurities.3. Through the programming, this thesis separately simulates the con diti ons that differe nt ofquantities,mass and elasticity coefficient of impurities aredoped into two-dimensional atomic chain system, and get the law of obstruct ing en ergy tran s

18、fer by impurities.This thesis use program ming to simulate the in flue nee of impurities on thermal con ductivity. The results show that:Doped within the system with the samequantity and the elasticity coefficient ratio of impurities, the mass ratio takes a set of values, bothon e-dime nsional model

19、 and two-dime nsional model will get the sameresult. The more similar of the massof impurity atoms and the mass of the substrate materials, the less help to reduce the thermal conductivity.Dopedwithin the system with the samequantity and the mass ratio of impurities, the elasticity coefficie nt rati

20、o 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 thermalconduction. Doped within the system with the samequantity and property of impurities, the more dispersed of impurities, the more help to reduce the thermal con ducti on