【摘要】：隨著化石能源的不斷消耗,人類的不可再生資源面臨嚴(yán)重問題。與此同時(shí),太陽能發(fā)電作為一種高效的發(fā)電方式,是一種非常有潛力的新能源發(fā)電技術(shù)。這其中涉及到兩種最常見也最主要的太陽能發(fā)電形式:光伏發(fā)電和光熱發(fā)電。太陽能熱發(fā)電最有別于光伏發(fā)電的地方在于每一個(gè)太陽能熱發(fā)電系統(tǒng)都標(biāo)準(zhǔn)配備有儲(chǔ)能部分,這就為用電的調(diào)峰過程提供了極大的便利。光熱發(fā)電是太陽能利用的高品位方式,通過匯集太陽能產(chǎn)生的輻射熱的形式,加熱水或者水蒸氣,推動(dòng)汽輪機(jī)轉(zhuǎn)動(dòng),帶動(dòng)發(fā)電機(jī)發(fā)電。太陽能轉(zhuǎn)換成電能要經(jīng)歷多次能量轉(zhuǎn)換的過程,而其中對(duì)熱能的合理利用,是光熱發(fā)電的關(guān)鍵技術(shù)。在太陽能熱發(fā)電系統(tǒng)中,傳熱儲(chǔ)熱工質(zhì)的選擇要面對(duì)非常多限制條件,包括低腐蝕性、較高的熱容和穩(wěn)定性、出色的導(dǎo)熱性能,還有重復(fù)利用性。熔鹽作為非常有前景的儲(chǔ)熱工質(zhì)得到了工業(yè)界的廣泛關(guān)注。本文力求在現(xiàn)有研究基礎(chǔ)上,探索熔融鹽在太陽能集熱蓄熱領(lǐng)域中作為蓄熱材料的可行性和可優(yōu)化性。本文將碳納米管加入鹽類等固體介質(zhì)中,形成的團(tuán)簇結(jié)構(gòu)和液膜層,大幅提升新型混合物熱物性。因此提出了一種新型儲(chǔ)熱材料:MWCNTs-太陽鹽復(fù)合材料,即多壁碳納米管-太陽鹽復(fù)合材料。并建立了其導(dǎo)熱率計(jì)算公式模型,同時(shí)親手制備MWCNTs-太陽鹽復(fù)合材料,并測(cè)量其包括導(dǎo)熱率在內(nèi)的多種熱物性,驗(yàn)證導(dǎo)熱率模型的準(zhǔn)確性。本文在制造此種新材料的同時(shí),對(duì)其導(dǎo)熱特性大幅提升的理論機(jī)理進(jìn)行了研究分析,整合多項(xiàng)修正因子來推演導(dǎo)熱系數(shù)的計(jì)算模型。該模型充分考慮了團(tuán)聚、顆粒分布、布朗運(yùn)動(dòng)形成的微對(duì)流(包括溫度變化對(duì)布朗運(yùn)動(dòng)的影響)等因素對(duì)納米流體導(dǎo)熱系數(shù)的影響。同時(shí)本文進(jìn)行了MWCNTs-太陽鹽復(fù)合材料的制備,并對(duì)其熔融狀態(tài)下的導(dǎo)熱率進(jìn)行測(cè)定,實(shí)際證明該模型能夠準(zhǔn)確預(yù)測(cè)出MWCNTs-太陽鹽復(fù)合材料高溫熔融條件下導(dǎo)熱系數(shù)增強(qiáng)的趨勢(shì),增強(qiáng)幅度最大可達(dá)49.1%,新的導(dǎo)熱率計(jì)算模型理論預(yù)測(cè)值與現(xiàn)有實(shí)驗(yàn)數(shù)據(jù)平均誤差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.
【學(xué)位授予單位】：華北電力大學(xué)(北京)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2017
【分類號(hào)】：TB383.1

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