聚光型纳米流体直接吸收式太阳能中温集热特性研究
发布时间：2018-11-23 08:52
【摘要】：太阳能中温集热系统应用于工业加热、驱动制冷空调和中温热发电等领域的需求巨大,替代传统化石燃料燃烧具有显著的节能环保优势。目前常规的太阳能中温集热器吸收涂层的高温耐久性差、聚光引起集热管局部受热而易发生弯曲变形损坏,导致制造和维护成本高,成为其应用的主要障碍。本文提出并研究一种聚光型纳米流体直接吸收太阳能集热器(NDASC),采用透明无涂层集热管,通过在集热流体(导热油)中添加吸热纳米颗粒,使其具有很强的太阳辐射吸收特性,用于太阳能中温集热。在对导热油/CuO纳米流体的光谱吸收特性研究基础上,探讨集热管内纳米流体直接吸收及热量传递机理,研究非均匀聚光工况下NDASC集热管内流体的温度分布与集热特性,主要工作如下：(1)配制了四种不同质量分数的导热油/CuO纳米流体,理论分析结合实验测试,研究了纳米流体的全光谱辐射吸收特性,以及粘度、热导率等基础热物性；并根据太阳辐射的能量分布,计算得出了纳米流体全光谱的平均吸收系数。(2)在对聚光器的光学特性、纳米流体吸热-传热过程机理分析基础上,建立了槽式聚光型NDASC的集热数学模型,并利用CFD软件对NDASC在非均匀聚光工况下的管内流体温度分布和集热性能进行了模拟,分析了添加纳米颗粒质量分数、太阳辐射强度、环境温度、集热流体入口温度等因素对集热特性的影响规律,得到了典型工况下的最佳质量分数。并且,对采用相同聚光器的NDASC和传统间接吸收太阳能集热器(IASC)进行了性能对比。结果表明：NDASC的管内纳米流体温度分布更加均匀,集热管壁面温差明显降低；并且在一定集热温度范围内,NDASC的集热效率要高于IASC。(4)搭建了槽式聚光型NDASC与IASC中温集热工况下的对比实验系统,进行典型工况下的实验测试。实验结果表明:NDASC的最大瞬时集热效率达62%,集热效率随集热温度升高而降低；在124.2℃集热温度范围内,效率高于IASC,验证了NDASC中温集热的可行性。(5)对复合抛物面聚光器(CPC)进行了光学特性分析,计算得到了集热管表面的辐射热流分布。在此基础上,模拟分析了CPC聚光型NDASC的内部温度分布特性和集热性能。结果表明,集热效率在入口温度低于106.7℃时优于传统IASC。
[Abstract]:The application of solar energy medium-temperature system in industrial heating, driving refrigeration, air conditioning and medium-temperature thermal power generation has a huge demand, replacing the traditional fossil fuel combustion has a significant advantage in energy saving and environmental protection. At present, the high temperature durability of the conventional solar collector absorbs the coating at high temperature, and the concentrated light causes local heating of the collector pipe, which is prone to bending deformation and damage, which leads to high manufacturing and maintenance costs, and becomes the main obstacle to its application. In this paper, we present and study the direct absorption of solar energy collector (NDASC), by adding endothermic nanoparticles into the collector fluid (heat conduction oil) by using transparent and uncoated collector tubes. It has strong absorption characteristics of solar radiation, and is used for solar energy moderate temperature heat collection. Based on the study of the spectral absorption characteristics of the thermal conductivity oil / CuO nanofluids, the mechanism of direct absorption and heat transfer of the nano-fluids in the collector tube is discussed, and the temperature distribution and the heat collecting characteristics of the fluid in the NDASC collector tube under the condition of non-uniform concentrating light are studied. The main works are as follows: (1) four kinds of thermal conductive oil / CuO nanofluids with different mass fraction were prepared. Theoretical analysis and experimental tests were used to study the absorption characteristics of full-spectrum radiation, viscosity, thermal conductivity and other basic thermal properties of nano-fluids. According to the energy distribution of solar radiation, the average absorption coefficient of the whole spectrum of nano-fluid is calculated. (2) based on the analysis of the optical properties of the condenser and the mechanism of endotherm-heat transfer process of nano-fluid, In this paper, the mathematical model of collecting heat of trough type NDASC is established, and the temperature distribution and heat collecting performance of NDASC are simulated by CFD software. The mass fraction of nano-particles and the intensity of solar radiation are analyzed. The influence of environmental temperature and inlet temperature of heat collecting fluid on the characteristics of heat collection is studied. The optimum mass fraction under typical working conditions is obtained. The performance of NDASC with the same concentrator is compared with that of the traditional indirect absorption solar collector (IASC). The results show that the temperature distribution of nanofluids in NDASC tubes is more uniform, and the temperature difference on the wall of collector tubes is obviously reduced. And in a certain temperature range, the heat collection efficiency of NDASC is higher than that of IASC. (4). A comparative experimental system of trough type NDASC and IASC is set up, and the experimental tests are carried out under typical conditions. The experimental results show that the maximum instantaneous heat collection efficiency of NDASC is 62%, and the heat collection efficiency decreases with the increase of collecting temperature. At the temperature range of 124.2 鈩，
本文编号：2350968
[Abstract]:The application of solar energy medium-temperature system in industrial heating, driving refrigeration, air conditioning and medium-temperature thermal power generation has a huge demand, replacing the traditional fossil fuel combustion has a significant advantage in energy saving and environmental protection. At present, the high temperature durability of the conventional solar collector absorbs the coating at high temperature, and the concentrated light causes local heating of the collector pipe, which is prone to bending deformation and damage, which leads to high manufacturing and maintenance costs, and becomes the main obstacle to its application. In this paper, we present and study the direct absorption of solar energy collector (NDASC), by adding endothermic nanoparticles into the collector fluid (heat conduction oil) by using transparent and uncoated collector tubes. It has strong absorption characteristics of solar radiation, and is used for solar energy moderate temperature heat collection. Based on the study of the spectral absorption characteristics of the thermal conductivity oil / CuO nanofluids, the mechanism of direct absorption and heat transfer of the nano-fluids in the collector tube is discussed, and the temperature distribution and the heat collecting characteristics of the fluid in the NDASC collector tube under the condition of non-uniform concentrating light are studied. The main works are as follows: (1) four kinds of thermal conductive oil / CuO nanofluids with different mass fraction were prepared. Theoretical analysis and experimental tests were used to study the absorption characteristics of full-spectrum radiation, viscosity, thermal conductivity and other basic thermal properties of nano-fluids. According to the energy distribution of solar radiation, the average absorption coefficient of the whole spectrum of nano-fluid is calculated. (2) based on the analysis of the optical properties of the condenser and the mechanism of endotherm-heat transfer process of nano-fluid, In this paper, the mathematical model of collecting heat of trough type NDASC is established, and the temperature distribution and heat collecting performance of NDASC are simulated by CFD software. The mass fraction of nano-particles and the intensity of solar radiation are analyzed. The influence of environmental temperature and inlet temperature of heat collecting fluid on the characteristics of heat collection is studied. The optimum mass fraction under typical working conditions is obtained. The performance of NDASC with the same concentrator is compared with that of the traditional indirect absorption solar collector (IASC). The results show that the temperature distribution of nanofluids in NDASC tubes is more uniform, and the temperature difference on the wall of collector tubes is obviously reduced. And in a certain temperature range, the heat collection efficiency of NDASC is higher than that of IASC. (4). A comparative experimental system of trough type NDASC and IASC is set up, and the experimental tests are carried out under typical conditions. The experimental results show that the maximum instantaneous heat collection efficiency of NDASC is 62%, and the heat collection efficiency decreases with the increase of collecting temperature. At the temperature range of 124.2 鈩，
本文编号：2350968
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