【作者】 赵佳飞；

【导师】 骆仲泱； 倪明江； 岑可法；

【作者基本信息】 浙江大学 ， 热能工程， 2009， 博士

【摘要】 能源是人类社会发展的原动力,也是人类赖以生存的基础。然而,随着近一个世纪来人类社会的快速发展,世界能源不断紧缺,全球环境也面临着前所未有的压力。开发新能源、发展新能源技术,成为了全球各国寻求可持续发展之路必须面临的问题和挑战。太阳能作为一种可再生的清洁能源蕴藏着巨大能量,太阳辐射到达地球表面的能量高达4×1015MW,约为全球能耗的2000倍,太阳能利用、太阳能材料相关技术的开发在世界范围内引起了重视。纳米材料作为一种新型的能源材料,由于纳米颗粒粒子尺寸与传导电子德布罗意波长以及超导态的相干波长物理尺寸相当甚至更小,其周期性边界条件受到破坏,同时粒径的变小表面效应急剧增大,纳米颗粒体现出了对辐射波的强吸收与选择性吸收特性。随着上世纪80年代研究者对纳米流体直接吸收太阳辐射技术(DAC)的提出,利用纳米颗粒的辐射特性,将纳米流体技术应用于太阳能利用中成为了新的热点能源技术。在对纳米流体辐射、纳米流体太阳能直接吸收利用技术、以及太阳能光热光电利用技术综述的基础上,本论文围绕纳米流体的辐射特性展开研究,并基于DAC技术将纳米流体应用于太阳能电热联用系统进行应用研究。纳米流体中颗粒的均匀和稳定分散是研究所有纳米流体问题的基础,本文首先从纳米流体的制备方法入手,采用一步法即化学法制备了不同粒径分布的球型单分散纳米流体,与二步法利用高压微射流制备了非单分散的纳米流体,并且分析不同方法制备的纳米流体的稳定特性,以及纳米颗粒与团聚体大小,为分析纳米流体辐射特性奠定基础条件。本文研究了纳米流体的体系辐射与纳米颗粒辐射。对比分析了辐射传递模型和有效介质模型,并且结合试验测试,采用不同的有效介质模型对纳米流体的有效光学参数进行了模拟计算,验证了对于纳米流体在不同粒径分布下不同有效介质模型的适用性。对于纳米流体中颗粒辐射特性,本文建立了消光、散射测试试验台,并且提出了“最值比方法”,该方法有效的避免了理论研究中对于测试系统中纳米颗粒数目的严重依赖性,建立起了试验测试与理论分析之间的桥梁,为分析纳米颗粒辐射特性提供了重要的有效途径。本文进而研究了纳米颗粒在两个不同的极限粒径下,纳米颗粒的自由电子相以及内部束缚电子相对于纳米颗粒辐射特性的影响,得到了金纳米颗粒在两个极限粒径下的辐射性能。针对辐射研究中常遇到的实际问题和工程需要,本文建立起了对于物质和物质体系辐射的反问题研究模型。该模型基于弥散理论的振动模型,利用PIKAIA遗传算法,计算结果自动满足Kramers-Kronig关系,确保了结果的物理真实性和高效性。该模型可以以期望的辐射性能出发反向计算,在工程应用中对反向寻找物质以及物质的辐射特性具有了重要的作用,这对太阳能热系统设计等应用研究有着重要的指导意义。本文利用纳米流体对于太阳能辐射直接吸收的技术(DAC),采用分光分波段利用太阳能辐射的思路设计了新型的太阳能电热联用系统,在该系统中光热单元利用纳米流体直接吸收太阳辐射红外波段能量进行光热转换,系统光电单元仅主要接收太阳辐射可见光波段能量完成光电转换。该系统中光热单元与光电单元分离,光热单元的热量不再依赖于光电单元,光热单元温度不再受到光电单元工作温度的限制,可以在确保光电效率的同时产生高温热能,同时避免传统电热联用系统中加工技术瓶颈问题。本文利用建立的辐射特性反问题研究模型,对设计的新型太阳能电热联用系统的纳米流体工质进行了反向计算,得到了纳米流体工质的有效光学常数,并且提出了利用现有纳米颗粒与基液的优化拟核方法,进而确定了在该太阳能电热联用系统中光热单元与光电单元的太阳光谱吸收率与平均吸收率。在此基础上本文建立了太阳能电热联用系统的辐射传递模型和能量平衡模型,对系统在非聚光与聚光条件下的性能进行了综合分析,分析包括了系统光电单元工作温度、系统光热单元产热温度、系统光电效率、系统光热效率、以及系统有效输出能效率。研究证明该新型太阳能电热联用系统由于采用了分光分波段直接利用太阳辐射能的设计思路,避免了传统电热联用系统五种局限,确保了系统具有高的光热效率光电效率以及有效输出能效率。更多还原

【Abstract】 Energy plays an important role in the development of human society. However, over the past century, the fast development of human society leads to the shortage of global energy and the serious environmental pollution. All countries of the world have to explore new energy sources and develop new energy technologies to find the rode to sustainable development.Solar energy as the renewable and environmental friendly energy, it has produced energy for billions of years. Solar energy that reaches the earth is around 4×1015MW, it is 2000 times as large as the global energy consumption. Thus the utilization of solar energy and the technologies of solar energy materials attract much more attention. Nano-materials as a new energy material, since its particle size is the same as or smaller than the wavelength of de Broglie wave and coherent wave. Particles’cyclical boundary condition is changed. Additionally, as the particle diameter decreases, the surface effect of nanoparticle increases sharply. Therefore, nanoparticle becomes to strongly absorb and selectively absorb incident radiation. Researchers present the direct solar radiation absorption collection (DAC) system concepts 1980s. Based on the radiation properties of nanoparticle, the utilization of nanofluids in solar thermal system becomes the new study hotspot.Based on the review of nanofluids radiation, direct absorption collection systems and solar energy utilizations, first the thesis discussed the ratiative heat transfer of nanofluids, then designed and analyzed the new Photovoltaic/Thermal system using the DAC technology. Because the premise of nanofluids research is even distribution and no sedimentation of nanofluids, in the thesis we used the one-step method to produce even distribution nanofluids, and two-step method to produce nonhomogeneous distribution nanofluids by the M-110S Microfluidizer Processor. The stability of nanofluis and the size of nanoparticle and aggregate were also studied, which lays the foundation for the nanofluid radiation research.The thesis studied the radiation properties of nanofluids system and nanopartcles, and compared the radiation transfer equation (RTE) and the effective medium theories. The effective optical constant of nanofluids was simulated by different effective medium models. The validity of these models for various nanofluids were analyzed in combination with the experiments. As for the radiation of nanoparticles, the extinction and scattering experiments bench were set up, and the "Maximum Ratio Method" was proposed first time. The method avoids the dependence of the number of experimental nanoparticles for the simulation. It can be as the bridge between experiment and simulation, and provide an easy way to study the nanoparticles radiation. Based on the method, the effects of free electron term and interband or bound electron term on the nanoparticles radiation properties were investigated.Aiming to solve the practical problems, the thesis innovatively developed an inverse method for radiation. Since, the method is based on the classical dispersion theory, and adopted the PIKAIA genetic algorithm, the retrieved results of optical constant automatically satisfy the Kramers-Kronig relation, and the retrieving process is robust and fast. The method can be started from the desired radiation properties such as desired reflectivity and absorptance et al. The method can be also used to determine the complex index of refraction, and it can serve as a guideline for designing solar thermal systems.Moreover, the thesis innovatively expands the DAC nanofluids technology to the Photovoltaic/Thermal system, and presents a new Photovoltaic/Thermal system. The new system separately utilizes the solar radiation to produce thermal energy and electricity, thanks to the working fluid absorbing infrared solar radiation and the transmitted visible radiation by the solar cell. Furthermore, the system consists of a thermal unit placed above a PV module and separated by an air gap of arbitrary thickness. Thus, the thermal unit is no longer extracting heat from the PV module, and has no temperature limitation of the PV module. The PV module need not glued to the thermal unit to avoid delamination concerns. In addition, the system can produce high temperature thermal energy with high electricity efficiency.Using the inverse method, the effective complex index of refraction of working fluid in the system was retrieved and optimized based on the effective medium model. The absorptance and average absorptance of the thermal unit and PV module were also calculated. Furthermore, the working temperature of thermal unit and PV module, the electrical and thermal efficiencies and the exergetic efficiency were studied based on the radiation transfer and energy conservation equations. The results indicated that the new Photovoltaic/Thermal system separately using the infrared and visible light to avoid the five limitations of traditional systems, the system has high electricity and thermal efficiencies and exergetic efficiency.更多还原