离子液体基纳米流体的辐射特性和光热转换性能研究

发布时间：2018-04-29 06:11

本文选题：太阳能利用 + 直接吸收式集热器　；参考：《华南理工大学》2015年硕士论文

【摘要】：光热利用是最为实用和有效的太阳能利用方式之一。太阳能集热器是太阳能热利用系统中的关键部件。与传统太阳能集热器相比,直接吸收式集热器具有热损失小、转化效率高的特点,是新型太阳能集热器的重要发展方向。本文致力于为适宜太阳能中温热利用的直接吸收式太阳能集热器开发高性能的集热流体,选择液态温度范围宽、热分解温度高的离子液体为基液,通过添加不同纳米材料来配制离子液体基纳米流体,系统研究了离子液体基纳米流体的辐射特性、热物性和光热转换性能。采用两步法,将平均粒径同为40 nm的铜、镍和碳包镍三种球形纳米粒子分别添加到离子液体[HMIM][NTf2]中,配制了三种纳米流体。测定了离子液体及其纳米流体的透射率,并考察了光程、纳米颗粒种类及其体积分数等因素对透射率的影响;结果表明,将体积分数极低(ppm级)的纳米粒子添加到离子液体中大幅提升其吸光性能;离子液体纳米流体的透射率随着光程的增加而降低,并且随着纳米颗粒体积分数的增加而降低。依据测定出的纳米流体透射率,采用比尔-朗伯定律,获得了纳米流体的消光系数,并将其与基于瑞利散射理论模型计算出的消光系数进行了对比;研究发现,碳包镍纳米流体的消光系数要高于铜和镍的纳米流体,这是因为碳包镍颗粒表面包覆的石墨碳在可见和近红外波段对光有着良好的吸收特性。鉴于石墨碳材料具有良好的光吸收特性,选用了纳米石墨粉、单壁碳纳米管和石墨烯三种碳纳米材料,分别将其添加到离子液体[BMIM]BF4中,配制了三种碳纳米流体;从室温到150 oC范围内测定了碳纳米流体的导热系数、比热容和粘度等热物性,并通过闷晒实验评价了其光热转换性能。结果表明,石墨型纳米碳材料的添加使离子液体的导热系数有明显提高;在相同质量分数情况下,石墨烯纳米流体的导热系数提升幅度最大;因碳纳米材料的比热小于离子液体,所以致使纳米流体的比热容略有下降;离子液体及其纳米流体的粘度随温度的升高而显著降低,这有利于它们在中温太阳能热利用领域中的应用;在闷晒过程中,碳纳米流体的升温速率明显高于基液,这源于碳纳米材料高的导热系数和优异的光吸收特性;在一个太阳的光强下,质量分数为0.01 wt%的石墨烯/离子液体纳米流体的闷晒温度为103.5 oC,相应的光热转换效率达到了26.6%,显示出石墨烯/离子液体纳米流体在直接吸收式集热器中具有良好的应用前景。
[Abstract]:Photothermal utilization is one of the most practical and effective solar energy utilization methods. Solar collector is a key component in solar thermal utilization system. Compared with the traditional solar collector, the direct absorption collector has the characteristics of small heat loss and high conversion efficiency, which is an important development direction of the new solar collector. The aim of this paper is to develop high performance collector fluid for direct absorption solar collector, which is suitable for thermal utilization of solar energy. The ionic liquid with wide range of liquid temperature and high thermal decomposition temperature is selected as base liquid. The radiation properties, thermal properties and photothermal conversion properties of ionic liquid-based nano-fluids were systematically studied by adding different nanomaterials to prepare ionic liquid-based nano-fluids. Three kinds of nano-fluids were prepared by two-step method, in which copper, nickel and carbon coated nickel were added to the ionic liquid [HMIM] [NTf2] with the same average particle size of 40 nm. The transmissivity of ionic liquids and their nano-fluids was measured, and the effects of optical path, kinds of nanoparticles and their volume fraction on the transmittance were investigated. The transmittance of ionic liquid nanoparticles decreases with the increase of optical path and decreases with the increase of volume fraction of nanoparticles. According to the measured transmittance of nano-fluid, the extinction coefficient of nano-fluid is obtained by using Beer-Lambert law, and compared with the extinction coefficient calculated based on Rayleigh scattering theory model. The extinction coefficient of carbon coated nickel nanofluids is higher than that of copper and nickel nanofluids, which is due to the good absorption characteristics of graphite carbon coated on the surface of carbon coated nickel particles in visible and near infrared bands. In view of the good light absorption properties of graphite carbon materials, three kinds of carbon nano-materials, such as nano-graphitic powder, single-walled carbon nanotubes and graphene, were added to the ionic liquid [BMIM] BF4 to prepare three kinds of carbon nano-fluids. The thermal conductivity, specific heat capacity and viscosity of carbon nanofluids were measured from room temperature to 150oC. The results showed that the thermal conductivity of ionic liquids was obviously increased with the addition of graphite-type nano-carbon materials, and the thermal conductivity of graphene nano-fluids was the largest at the same mass fraction. Because the specific heat of carbon nanomaterials is smaller than that of ionic liquids, the specific heat capacity of nanofluids decreases slightly, and the viscosity of ionic liquids and their nanofluids decrease significantly with the increase of temperature. This is beneficial to their application in the field of thermal utilization of medium-temperature solar energy, and the heating rate of carbon nano-fluid is obviously higher than that of base solution in the process of sun-stuffing, which is due to the high thermal conductivity and excellent light absorption characteristics of carbon nano-materials. In the light of a sun, The solder temperature of graphene / ionic liquid nano-fluid with a mass fraction of 0.01wt% is 103.5 OC, and the corresponding photothermal conversion efficiency reaches 26.6wt%, which shows that graphene / ionic liquid nano-fluid has a good application prospect in direct absorption collector.
【学位授予单位】：华南理工大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TB383.1

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