离子液体基纳米流体导热系数的分子动力学模拟

发布时间：2018-03-12 08:17

本文选题：纳米流体　切入点：离子液体　出处：《大连理工大学》2015年硕士论文　论文类型：学位论文

【摘要】：吸收式热泵是一种利用余热来实现低温向高温输送热量的节能环保设备。传统的热泵工质对有氨水和溴化锂水溶液,但是氨水有毒,溴化锂水溶液则易结晶和腐蚀设备。离子液体是一种新型的绿色有机溶剂,具有蒸汽压低,液程宽,热稳定及无腐蚀性等特点,而且具有替代传统热泵工质成为吸收制冷或吸收热泵冷媒新型吸收剂的可能。纳米流体是一种悬浮有纳米粒子或纳米管而形成的新型冷却工质,相比较于传统的流体,纳米流体具有异乎寻常的热传递性能。将离子液体基纳米流体作为热泵新工质不仅能强化传热,而且具备离子液体独特的性能。本文主要利用分子动力学模拟方法,以传统的水基纳米流体为出发点,研究了新型离子液体基纳米流体作为热泵工质的传热特性。具体工作和成果如下：第一部分：利用分子动力学方法模拟计算了四种常见水模型的密度、粘度、扩散系数和导热系数,结果表明SPC/E水模型的模拟值与实验值吻合较好。在此基础上,我们选择SPC/E水模型作为水基纳米流体的基液,计算了加入纳米铜颗粒后的水基纳米流体导热系数,并与实验值进行比较吻合较好。第二部分：利用量化方法对离子液体进行几何构型优化、频率分析和能量计算,选择出最稳定的离子液体构型,并得到相应的结构参数和原子电荷,又采用OPLS和Amber混合力场来分别描述离子液体阴阳离子,从而建立起离子液体的力场。为了验证离子液体力场的准确性,采用分子动力学方法模拟了离子液体在不同温度下的密度、扩散系数和导热系数,验证了力场的准确性。最后,为研究同一纳米颗粒不同质量分数以及同一质量分数不同纳米颗粒的离子液体基纳米流体导热系数,建立了各种纳米流体模型,结果表明：各离子液体基纳米流体的导热系数相比于离子液体均有提高。第三部分：为了工业应用的目的,我们首先模拟计算了不同摩尔分数下的离子液体二元溶液的密度、扩散系数和导热系数。接着模拟计算了以纳米铜颗粒为添加剂的离子液体二元溶液基纳米流体的导热系数,并较其基液二元溶液的导热系数有所提高。第四部分：为了探究纳米流体导热系数增加的原因,我们分析了加入纳米颗粒前后各粒子运动的快慢、微观结构变化和导热系数中各项贡献大小。结果表明：维里自相关项在纳米流体导热系数的提高当中起到了最大的积极作用。
[Abstract]:Absorption heat pump is a kind of energy saving and environmental protection equipment that uses waste heat to transfer heat from low temperature to high temperature. Traditional heat pump working fluid has ammonia water and lithium bromide aqueous solution, but ammonia water is poisonous. Ionic liquids are a new green organic solvent with the characteristics of low vapor pressure, wide liquid range, thermal stability and non-corrosive properties. In addition, it is possible to replace the traditional heat pump refrigerant as a new absorbent for the absorption of refrigeration or heat pump refrigerant. Nano-fluid is a new type of refrigerant formed by suspending nanoparticles or nanotubes, compared with the traditional fluid. Nano-fluids have extraordinary heat transfer properties. Using ionic liquid-based nano-fluids as a new working medium of heat pump can not only enhance heat transfer, but also possess unique properties of ionic liquids. Starting from traditional water-based nanofluids, The heat transfer characteristics of new ionic liquid-based nano-fluids as working fluid of heat pump are studied. The results are as follows: part one: the density and viscosity of four common water models are simulated and calculated by molecular dynamics method. The results of diffusion coefficient and thermal conductivity show that the simulated value of SPC/E water model is in good agreement with the experimental value. On this basis, we choose the SPC/E water model as the base liquid of water-based nano-fluid. The thermal conductivity of water-based nanoscale fluids after adding nano-copper particles is calculated, and it is in good agreement with the experimental data. Part two: the geometric configuration optimization, frequency analysis and energy calculation of ionic liquids are carried out by using quantization method. The most stable configuration of ionic liquids is selected and the corresponding structure parameters and atomic charges are obtained. The mixed force fields of OPLS and Amber are used to describe the anion and anion of ionic liquids, respectively. In order to verify the accuracy of the ionic liquid force field, the density, diffusion coefficient and thermal conductivity of the ionic liquid at different temperatures were simulated by molecular dynamics method, and the accuracy of the force field was verified. In order to study the thermal conductivity of ionic liquid-based nano-fluids with different mass fraction and different mass fraction of the same nanoparticles, a variety of nano-fluid models were established. The results show that the thermal conductivity of each ionic liquid-based nano-fluid is higher than that of ionic liquid. Part three: for the purpose of industrial application, we first simulate and calculate the density of ionic liquid binary solution with different molar fraction. Diffusion coefficient and thermal conductivity. Then the thermal conductivity of ionic liquids based on binary solution with nano-copper particles as additive was simulated. In part 4th, in order to explore the reasons for the increase of thermal conductivity of nano-fluids, we analyzed the speed of the motion of each particle before and after the addition of nano-particles. The results show that the virion autocorrelation term plays the most active role in the increase of thermal conductivity of nanoscale fluids.
【学位授予单位】：大连理工大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TQ021.1

【参考文献】