本文選題：納米流體 + 導熱系數(shù)�。� 參考：《青島科技大學》2015年碩士論文

【摘要】：隨著全世界能源消耗量增加與資源短缺之間的矛盾日益加劇以及環(huán)境污染日益嚴重,尋求低耗能、低污染工業(yè)產(chǎn)業(yè)的呼聲越來越高。納米粒子作為一種具有特殊性能的物質(zhì)成為研究者研究的熱點,并逐漸被應用于各行業(yè)中。將納米粒子均勻分散于基液中,制備出性能穩(wěn)定的新型換熱工質(zhì),是提高換熱設(shè)備換熱能力的重要舉措。本文將兩種納米粒子添加到濃度為50%的溴化鋰溶液中,采用“兩步法”制備分散性能優(yōu)異的納米流體。采用自制的熱探針式導熱儀測試了納米流體的導熱系數(shù)。用烏氏粘度計測量了納米流體的粘度。采用重力沉降法觀察了納米流體的穩(wěn)定性。實驗結(jié)果表明,納米粒子濃度與分散劑的添加量是影響納米流體導熱性能及粘度的重要影響因素。隨著納米粒子質(zhì)量分數(shù)的增加,納米流體導熱系數(shù)跟粘度均呈現(xiàn)先逐漸增加后趨于平緩并略有下降的趨勢。阿拉伯膠添加量對液體粘度的影響明顯大于納米粒子。溴化鋰溶液中添加CNT納米粒子質(zhì)量分數(shù)為1.0%,阿拉伯膠添加量為0.4%時,納米流體導熱系數(shù)增加了約22%。設(shè)計組建了單管噴淋換熱系統(tǒng)實驗臺,研究分析了噴淋密度、溫度、管間距以及碳納米管濃度等因素對納米流體噴淋換熱性能的影響。實驗結(jié)果表明,管間距、噴淋密度、熱水溫度、CNT濃度等因素對管外平均換熱系數(shù)均有影響。隨著噴淋密度跟管間距的增大,管外平均換熱系數(shù)均先增大后降低；當管間距為換熱管管徑的1.2倍,噴淋密度為Γ=0.0833～0.104kg/(ms)時,效果最佳。隨著CNT納米粒子濃度的增加,管外平均換熱系數(shù)先逐漸增大,后趨于平穩(wěn)。當添加的質(zhì)量分數(shù)為0.8%時,管外平均換熱系數(shù)增加了31%。在溴化鋰溶液中添加CNT納米粒子能顯著提高液體的導熱、換熱性能。建立了水平管外降膜流動的二維模型,模擬了溴化鋰溶液在水平管外的降膜流動特性。研究分析了噴淋密度、管間距以及管徑對降膜流動的影響。結(jié)果表明,管間距、噴淋密度和管徑對液膜分布及液膜厚度均有不同程度的影響。采用合適的管間距和噴淋密度才能使換熱系統(tǒng)性能達到最優(yōu)。
[Abstract]:With the increasing contradiction between the increasing energy consumption and the shortage of resources and the increasingly serious environmental pollution, there is a growing demand for low energy consumption and low pollution industrial industries. As a kind of material with special properties, nanoparticles have become the research hotspot of researchers, and have been gradually applied in various industries. It is an important measure to improve the heat transfer capacity of heat transfer equipment by uniformly dispersing nanoparticles in the base solution to prepare new heat exchanger with stable performance. In this paper, two kinds of nanoparticles were added to 50% lithium bromide solution to prepare nano-fluid with excellent dispersion performance by "two-step method". The thermal conductivity of nanofluids was measured by a self-made thermal probe thermal conductivity instrument. The viscosity of nanoscale fluid was measured by using the Wurtzian viscometer. The stability of nanoscale fluid was observed by gravity sedimentation method. The experimental results show that the concentration of nanoparticles and the amount of dispersant are important factors affecting the thermal conductivity and viscosity of nano-fluids. With the increase of the mass fraction of nano-particles, the thermal conductivity and viscosity of nano-fluids increase gradually and then gradually decrease. The effect of Arabic gum addition on the viscosity of liquid is obviously greater than that of nanoparticles. When the mass fraction of CNT nanoparticles in lithium bromide solution is 1.0 and the amount of Arabic gum is 0.4, the thermal conductivity of nano-fluids increases by about 22g. A single tube spray heat transfer system was designed and constructed, and the effects of spray density, temperature, tube spacing and carbon nanotube concentration on the spray heat transfer performance of nano-fluid were studied and analyzed. The experimental results show that the average heat transfer coefficient outside the tube is affected by such factors as tube spacing, spray density and CNT concentration of hot water. With the increase of spray density and tube spacing, the average heat transfer coefficient first increases and then decreases, and the effect is the best when the tube spacing is 1.2 times of the diameter of the heat exchanger tube and the spray density is 螕 0.0833 ~ 0.104 kg 路s ~ (-1) 路m ~ (-1). With the increase of the concentration of CNT nanoparticles, the average heat transfer coefficient firstly increases gradually, and then tends to steady. When the mass fraction is 0.8, the average heat transfer coefficient increases by 31. The addition of CNT nanoparticles in lithium bromide solution can significantly improve the thermal conductivity and heat transfer properties of the liquid. A two-dimensional model of falling film flow outside a horizontal tube was established, and the falling film flow characteristics of lithium bromide solution outside the horizontal tube were simulated. The effects of spray density, tube spacing and pipe diameter on the falling film flow are studied and analyzed. The results show that the distance between tubes, spray density and diameter have different effects on the distribution and thickness of liquid film. The optimal performance of the heat transfer system can be achieved by adopting proper pipe spacing and spray density.
【學位授予單位】：青島科技大學
【學位級別】：碩士
【學位授予年份】：2015
【分類號】：TB383.1

【參考文獻】

相關(guān)期刊論文 前1條

1 黎陽;謝華清;王繼芬;陳立飛;于偉;;幾種氧化物納米流體強化傳熱性能研究[J];工程熱物理學報;2011年03期

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本文編號：1968828