【摘要】：在液體中添加納米級的金屬或金屬氧化物粒子制備成納米流體,具有優(yōu)異的熱傳輸性能以及良好的光譜吸收性能,將其用作直接吸收式太陽能集熱器的集熱工質(zhì),可有效提高光熱利用效率。本文以不同形貌Ag-EG納米流體為研究對象,研究了納米流體的合成方法,分析了其導熱性能、粘度、潤濕性能以及光熱特性等物理性能,主要研究內(nèi)容如下:1.采用多元醇法成功制備了立方狀以及不同粒徑的線狀Ag-EG納米流體;采用晶種法制備了銀納米棒,通過超聲振動將其分散到EG中,制備出棒狀Ag-EG納米流體。并通過XRD、SEM以及TEM等分析測試技術(shù)對三種形貌的Ag-EG納米流體進行了表征。2.采用KD2 Pro導熱系數(shù)儀測量了Ag-EG納米流體的導熱系數(shù),并分析了溫度、質(zhì)量分數(shù)、顆粒粒徑及形貌對其導熱系數(shù)的影響。結(jié)果表明,隨著溫度升高,Ag-EG納米流體的導熱系數(shù)增大,當溫度從25℃升高到65℃時,導熱系數(shù)最大增大率為48.60%;隨著質(zhì)量分數(shù)增大,導熱系數(shù)增大,其中立方狀Ag-EG納米流體增大率可達57.99%;同樣,粒徑和形貌也是影響導熱系數(shù)的兩個因素,立方狀Ag-EG納米流體的導熱系數(shù)最大,其次為棒狀、線狀Ag-EG納米流體;通過對不同粒徑的線狀Ag-EG納米流體的導熱系數(shù)進行分析,發(fā)現(xiàn)粒徑越小,導熱系數(shù)越大。最后,本文將實驗值與理論模型模型的計算值進行比較,發(fā)現(xiàn)實驗值與H-C模型計算出的理論值基本吻合,誤差最小為0.18%。3.采用DV2T粘度計對Ag-EG納米流體的粘度進行了測試,并研究了溫度、質(zhì)量分數(shù)、銀納米顆粒的粒徑以及形貌對其粘度的影響。實驗結(jié)果表明,隨著溫度的升高,Ag-EG納米流體的粘度減小,當溫度從25℃升高到65℃時,粘度減小率均在50%以上;銀納米顆粒質(zhì)量分數(shù)增大,粘度增大;通過對不同粒徑線狀納米流體的粘度進行對比分析發(fā)現(xiàn),隨著粒徑的減小,納米流體的粘度增大;立方狀Ag-EG納米流體的粘度要小于棒狀以及線狀Ag-EG納米流體。在65℃條件下,質(zhì)量分數(shù)為0.020wt.%時,立方狀Ag-EG納米流體的粘度為6.83mPa·s,相對于基液EG增大了9.80%�；诖�,本文將實驗值與理論模型模型的計算值進行比較,發(fā)現(xiàn)實驗值與Godson模型計算出的理論值最為接近。4.對Ag-EG納米流體的潤濕性進行了測試,通過表面張力和接觸角兩個方面進行研究,分析了溫度、質(zhì)量分數(shù)、顆粒粒徑以及形貌對Ag-EG納米流體表面張力和接觸角的影響,結(jié)果發(fā)現(xiàn),Ag-EG納米流體的表面張力和接觸角均小于基液EG,納米流體的潤濕性均優(yōu)于基液EG。其中,立方狀Ag-EG納米流體的表面張力和接觸角均為最小,質(zhì)量分數(shù)為0.020wt.%時,立方狀Ag-EG納米流體的表面張力在65℃的條件下為45.042mN/m,25℃時接觸角為27.5°。5.采用UV-5500紫外可見分光光度計測試Ag-EG納米流體的透射率,并自行組裝悶曬集熱裝置研究Ag-EG納米流體的悶曬溫度隨環(huán)境溫度的變化情況,分析納米流體質(zhì)量分數(shù)、納米顆粒粒徑和形貌對其光譜吸收性能和光熱轉(zhuǎn)換性能的影響。實驗結(jié)果表明,納米流體的光熱轉(zhuǎn)換特性優(yōu)于EG,且當質(zhì)量分數(shù)從0.005wt.%增大到0.015wt.%時,納米流體的最高平衡溫度和溫升速率均增大,但是當質(zhì)量分數(shù)繼續(xù)增加到0.020wt.%時光熱轉(zhuǎn)換特性反而下降。其中,立方狀納米流體的光熱特性最好,與基液EG的最大溫差為12℃,最高平衡溫度相對于基液EG提高了26.64%。
[Abstract]:The nano-fluid is prepared by adding nano-scale metal or metal oxide particles in a liquid, has excellent heat transfer performance and good spectral absorption performance, and can be used as a heat-collecting working medium of a direct absorption type solar heat collector, and the photo-thermal utilization efficiency can be effectively improved. In this paper, the synthesis of nano-fluid is studied by using Ag-EG nano-fluid with different morphology. The physical properties such as thermal conductivity, viscosity, wettability and photothermal properties of the nano-fluid are analyzed. The main contents of this study are as follows:1. The linear Ag-EG nano-fluid with cubic and different particle size was successfully prepared by using the polyol method, and the silver nanorod was prepared by the seed crystal method. The rod-shaped Ag-EG nano-fluid was prepared by dispersing it into EG by means of ultrasonic vibration. The Ag-EG nano-fluid was characterized by XRD, SEM and TEM. The thermal conductivity of Ag-EG nano-fluid was measured by the KD2 Pro thermal conductivity meter, and the influence of temperature, mass fraction, particle size and morphology on the thermal conductivity was also analyzed. The results show that, with the increase of the temperature, the thermal conductivity of the Ag-EG nano-fluid is increased, and when the temperature is raised from 25 鈩，

本文編號：2487945