纳米复合材料（MWCNTs-太阳盐）导热率实验与机理研究

发布时间：2018-09-11 20:24

【摘要】：随着化石能源的不断消耗,人类的不可再生资源面临严重问题。与此同时,太阳能发电作为一种高效的发电方式,是一种非常有潜力的新能源发电技术。这其中涉及到两种最常见也最主要的太阳能发电形式:光伏发电和光热发电。太阳能热发电最有别于光伏发电的地方在于每一个太阳能热发电系统都标准配备有储能部分,这就为用电的调峰过程提供了极大的便利。光热发电是太阳能利用的高品位方式,通过汇集太阳能产生的辐射热的形式,加热水或者水蒸气,推动汽轮机转动,带动发电机发电。太阳能转换成电能要经历多次能量转换的过程,而其中对热能的合理利用,是光热发电的关键技术。在太阳能热发电系统中,传热储热工质的选择要面对非常多限制条件,包括低腐蚀性、较高的热容和稳定性、出色的导热性能,还有重复利用性。熔盐作为非常有前景的储热工质得到了工业界的广泛关注。本文力求在现有研究基础上,探索熔融盐在太阳能集热蓄热领域中作为蓄热材料的可行性和可优化性。本文将碳纳米管加入盐类等固体介质中,形成的团簇结构和液膜层,大幅提升新型混合物热物性。因此提出了一种新型储热材料:MWCNTs-太阳盐复合材料,即多壁碳纳米管-太阳盐复合材料。并建立了其导热率计算公式模型,同时亲手制备MWCNTs-太阳盐复合材料,并测量其包括导热率在内的多种热物性,验证导热率模型的准确性。本文在制造此种新材料的同时,对其导热特性大幅提升的理论机理进行了研究分析,整合多项修正因子来推演导热系数的计算模型。该模型充分考虑了团聚、颗粒分布、布朗运动形成的微对流(包括温度变化对布朗运动的影响)等因素对纳米流体导热系数的影响。同时本文进行了MWCNTs-太阳盐复合材料的制备,并对其熔融状态下的导热率进行测定,实际证明该模型能够准确预测出MWCNTs-太阳盐复合材料高温熔融条件下导热系数增强的趋势,增强幅度最大可达49.1%,新的导热率计算模型理论预测值与现有实验数据平均误差5.79%。
[Abstract]:With the constant consumption of fossil energy, human non-renewable resources are faced with serious problems. At the same time, solar power generation as an efficient power generation, is a very potential new energy generation technology. This involves two of the most common and most important forms of solar power generation: photovoltaic and photothermal power generation. The most important difference between solar thermal generation and photovoltaic power generation is that every solar thermal power generation system is equipped with a standard energy storage part, which provides great convenience for the peak regulation process. Photothermal power generation is a high-grade way of solar energy utilization. By collecting the radiation heat generated by solar energy, heating water or water vapor, the steam turbine can be driven to rotate and drive the generator to generate electricity. The process of converting solar energy to electric energy has to go through many times, and the rational utilization of heat energy is the key technology of photothermal power generation. In the solar thermal power generation system, the selection of heat transfer and thermal storage fluid has many limitations, including low corrosion, high heat capacity and stability, excellent thermal conductivity, and reusability. Molten salt, as a very promising thermal storage medium, has attracted wide attention in industry. Based on the existing research, the feasibility and optimizability of molten salt as heat storage materials in the field of solar energy collection and storage are explored in this paper. In this paper, carbon nanotubes (CNTs) were added to solid media such as salts to form clusters and liquid film layers, which greatly improved the thermal properties of the new mixture. Therefore, a new type of thermal storage material, the multi-wall carbon nanotube-solar salt composite, is proposed. At the same time, MWCNTs- solar salt composites were prepared by hand, and their thermal properties, including thermal conductivity, were measured to verify the accuracy of the thermal conductivity model. In this paper, the theoretical mechanism of the thermal conductivity is studied and analyzed while the new material is manufactured, and the calculation model of thermal conductivity is deduced by integrating several correction factors. The influence of agglomeration, particle distribution and micro-convection formed by Brownian motion (including the effect of temperature on Brownian motion) on the thermal conductivity of nanoscale fluids is fully considered in the model. At the same time, the preparation of MWCNTs- solar salt composite is carried out, and the thermal conductivity of MWCNTs- solar salt composite under melting state is measured. It is proved that the model can accurately predict the increasing trend of thermal conductivity of MWCNTs- solar salt composite under the condition of high temperature melting. The maximum enhancement amplitude can be up to 49.1, and the average error between the theoretical prediction value of the new thermal conductivity calculation model and the existing experimental data is 5.79.
【学位授予单位】：华北电力大学(北京)
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TB383.1

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