發(fā)布時間：2018-04-29 06:11

  本文選題：太陽能利用 + 直接吸收式集熱器��； 參考：《華南理工大學》2015年碩士論文

【摘要】：光熱利用是最為實用和有效的太陽能利用方式之一。太陽能集熱器是太陽能熱利用系統(tǒng)中的關鍵部件。與傳統(tǒng)太陽能集熱器相比,直接吸收式集熱器具有熱損失小、轉(zhuǎn)化效率高的特點,是新型太陽能集熱器的重要發(fā)展方向。本文致力于為適宜太陽能中溫熱利用的直接吸收式太陽能集熱器開發(fā)高性能的集熱流體,選擇液態(tài)溫度范圍寬、熱分解溫度高的離子液體為基液,通過添加不同納米材料來配制離子液體基納米流體,系統(tǒng)研究了離子液體基納米流體的輻射特性、熱物性和光熱轉(zhuǎn)換性能。采用兩步法,將平均粒徑同為40 nm的銅、鎳和碳包鎳三種球形納米粒子分別添加到離子液體[HMIM][NTf2]中,配制了三種納米流體。測定了離子液體及其納米流體的透射率,并考察了光程、納米顆粒種類及其體積分數(shù)等因素對透射率的影響;結果表明,將體積分數(shù)極低(ppm級)的納米粒子添加到離子液體中大幅提升其吸光性能;離子液體納米流體的透射率隨著光程的增加而降低,并且隨著納米顆粒體積分數(shù)的增加而降低。依據(jù)測定出的納米流體透射率,采用比爾-朗伯定律,獲得了納米流體的消光系數(shù),并將其與基于瑞利散射理論模型計算出的消光系數(shù)進行了對比;研究發(fā)現(xiàn),碳包鎳納米流體的消光系數(shù)要高于銅和鎳的納米流體,這是因為碳包鎳顆粒表面包覆的石墨碳在可見和近紅外波段對光有著良好的吸收特性。鑒于石墨碳材料具有良好的光吸收特性,選用了納米石墨粉、單壁碳納米管和石墨烯三種碳納米材料,分別將其添加到離子液體[BMIM]BF4中,配制了三種碳納米流體;從室溫到150 oC范圍內(nèi)測定了碳納米流體的導熱系數(shù)、比熱容和粘度等熱物性,并通過悶曬實驗評價了其光熱轉(zhuǎn)換性能。結果表明,石墨型納米碳材料的添加使離子液體的導熱系數(shù)有明顯提高;在相同質(zhì)量分數(shù)情況下,石墨烯納米流體的導熱系數(shù)提升幅度最大;因碳納米材料的比熱小于離子液體,所以致使納米流體的比熱容略有下降;離子液體及其納米流體的粘度隨溫度的升高而顯著降低,這有利于它們在中溫太陽能熱利用領域中的應用;在悶曬過程中,碳納米流體的升溫速率明顯高于基液,這源于碳納米材料高的導熱系數(shù)和優(yōu)異的光吸收特性;在一個太陽的光強下,質(zhì)量分數(shù)為0.01 wt%的石墨烯/離子液體納米流體的悶曬溫度為103.5 oC,相應的光熱轉(zhuǎn)換效率達到了26.6%,顯示出石墨烯/離子液體納米流體在直接吸收式集熱器中具有良好的應用前景。
[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.
【學位授予單位】：華南理工大學
【學位級別】：碩士
【學位授予年份】：2015
【分類號】：TB383.1

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本文編號：1818728