發(fā)布時間：2018-05-22 16:50

  本文選題：納米流體 + 沸騰換熱系數(shù)　； 參考：《江蘇科技大學(xué)》2017年碩士論文

【摘要】：近年來,電子器件體積日趨小型化和集成化,單位面積的熱量集聚嚴重,由此引起的散熱問題日益嚴俊,如何實現(xiàn)熱量的高效傳遞以保證大功率電器的安全運行,一直困擾著相關(guān)領(lǐng)域的研究者。關(guān)于納米流體汽液兩相流強化傳熱方面的研究結(jié)論,在當今傳熱學(xué)領(lǐng)域仍存在較大爭議;且由于它在實際應(yīng)用中需求較大,促使各國相關(guān)領(lǐng)域研究者對其進行實驗研究和理論分析,但大部分僅局限于理論研究方面,實驗研究相對較少,因而本文希望通過實驗研究的方法,探討影響納米流體沸騰換熱性能的實驗機理,為實現(xiàn)更高效率的強化傳熱作鋪墊。本文在綜述了目前國內(nèi)外納米流體沸騰換熱的研究及其進展情況的基礎(chǔ)上,對納米流體進行了沸騰換熱實驗研究,探討其中蘊含的傳熱機理,為進一步強化沸騰換熱提供參考依據(jù)。首先采用兩步法制備了不同組分的納米流體,對其導(dǎo)熱系數(shù)等物性參數(shù)的影響因素進行了理論分析。然后,精心設(shè)計并搭建了納米流體沸騰換熱的實驗裝置,并結(jié)合已有的且研究比較成熟的水的沸騰換熱曲線,驗證了實驗裝置的可靠性及可重復(fù)性。進而介紹了具體的實驗方案及實驗方法,對不同納米流體的沸騰換熱特性進行實驗研究,利用高速攝像機對沸騰換熱過程進行了可視化觀測,記錄沸騰蒸發(fā)腔內(nèi)氣泡變化規(guī)律及相關(guān)試驗數(shù)據(jù),并對沸騰換熱前后加熱銅柱的上壁面情況進行了SEM表征對比。通過實驗數(shù)據(jù)、氣泡圖像、壁面形態(tài)等信息的整理,對比分析不同基液組分、納米顆粒濃度、納米顆粒粒徑、納米顆粒種類在不同系統(tǒng)運行壓力下的沸騰換熱特性的差異,進而分析以上各因素對納米流體沸騰換熱性能的影響及其作用機理。本文實驗研究結(jié)果表明:(1)在低濃度范圍內(nèi),納米顆粒質(zhì)量濃度越大,越有利于納米流體沸騰換熱性能的提高。納米顆粒平均粒徑為30nm,質(zhì)量濃度分別為0.001%、0.005%、0.01%的水-氧化鋁納米流體的沸騰換熱性能從左到右依次變大。(2)納米流體的沸騰換熱性能與納米顆粒種類有關(guān),在其他條件相同的情況下,納米顆粒的物性,諸如導(dǎo)熱系數(shù)、比熱、密度、粘度等,均會影響納米流體的沸騰換熱性能。納米顆粒平均粒徑為30nm、質(zhì)量濃度為0.005%的水-氧化鋁納米流體的沸騰換熱性能比水-二氧化硅更好。(3)對于制備納米流體的基液,也會影響納米流體的沸騰換熱性能。納米顆粒平均粒徑為30nm、質(zhì)量濃度為0.005%的氧化鋁納米流體,混合基液中乙二醇的質(zhì)量分數(shù)越低,納米流體的沸騰換熱性能越好。(4)在試驗范圍內(nèi),納米顆粒的平均粒徑越小,納米流體的沸騰換熱性能越好。質(zhì)量濃度均為0.005%,平均粒徑為30nm的水-氧化鋁納米流體的沸騰換熱性能優(yōu)于平均粒徑為50nm的水-氧化鋁納米流體。(5)試驗系統(tǒng)的工作壓力對納米流體的沸騰換熱性能有重要影響。實驗結(jié)果表明,與高壓條件相比,納米流體在低壓條件下的沸騰換熱性能更好。
[Abstract]:In recent years, the volume of electronic devices is becoming smaller and more integrated, the heat concentration per unit area is serious, and the heat dissipation problem is becoming more and more serious. How to achieve efficient heat transfer to ensure the safe operation of high-power electrical appliances, Researchers have been puzzling researchers in related fields. The conclusion of the research on the enhancement of heat transfer in the vapor liquid two phase flow of nanoscale fluid is still controversial in the field of heat transfer at present, and because of its great demand in practical application, However, most of them are confined to the theoretical research, and the experimental research is relatively few. Therefore, this paper hopes to adopt the method of experimental research. The experimental mechanism affecting the boiling heat transfer performance of nanofluids is discussed in order to pave the way for a more efficient enhancement of heat transfer. In this paper, based on the review of the research and progress of boiling heat transfer of nanofluids at home and abroad, the boiling heat transfer experiments of nanofluids are carried out, and the heat transfer mechanism is discussed. It provides reference for further enhancement of boiling heat transfer. In this paper, two step method was used to prepare different components of nanoscale fluids, and the influence factors of physical parameters such as thermal conductivity were analyzed theoretically. Then, the experimental apparatus of boiling heat transfer of nano-fluid is designed and built carefully, and the reliability and repeatability of the experimental device are verified by combining the existing boiling heat transfer curves of water with more mature research. Then the specific experimental scheme and experimental method are introduced. The boiling heat transfer characteristics of different nano-fluids are experimentally studied. The visualization observation of boiling heat transfer process is carried out by using high-speed video camera. The change of bubble in boiling evaporation chamber and related experimental data were recorded, and the SEM characterization of the upper wall of heated copper column before and after boiling heat transfer was carried out. Based on the experimental data, bubble images, wall morphology and other information, the differences of boiling heat transfer characteristics of different base liquid components, concentration of nanoparticles, particle size, and kinds of nanoparticles under different operating pressures were analyzed. The effect of these factors on the boiling heat transfer of nano-fluid and its mechanism are analyzed. The experimental results show that the higher the mass concentration of nanocrystalline particles is, the better the boiling heat transfer property of nanofluids is. The boiling heat transfer properties of water-alumina nanofluids with an average particle size of 30 nm and a mass concentration of 0.001% increase from left to right.) the boiling heat transfer properties of nano-fluids are related to the type of nanoparticles, and the other conditions are the same. The physical properties of nanoparticles, such as thermal conductivity, specific heat, density, viscosity and so on, will affect the boiling heat transfer properties of nano-fluids. The boiling heat transfer property of water-alumina nanofluid with 0.005% mass concentration is better than that of water-silica nanofluid. The average particle size is 30 nm and the concentration is 0.005%. The lower the mass fraction of ethylene glycol in the mixture solution, the better the boiling heat transfer property of nano-fluid. The better the boiling heat transfer of nanometer fluid. The boiling heat transfer of water-alumina nano-fluid with average diameter of 30nm is better than that of water-alumina nano-fluid with average diameter of 50nm. The working pressure of the system has an important effect on the boiling heat transfer of nano-fluid. The experimental results show that the boiling heat transfer performance of nanofluids at low pressure is better than that under high pressure.
【學(xué)位授予單位】：江蘇科技大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2017
【分類號】：TB383.1;TK124

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