摘 要
隨著熱管在生產(chǎn)和生活的各個(gè)領(lǐng)域被廣泛應(yīng)用，人們對(duì)于熱管的研究也越來(lái)越深入并提出了很多方法來(lái)提高熱管的傳熱效率；近年來(lái)，納米技術(shù)快速發(fā)展并在強(qiáng)化傳熱領(lǐng)域得到應(yīng)用。因此，將納米流體與熱管技術(shù)相結(jié)合，研究新型熱管，在理論上存在可行性。
本文將納米流體作為熱管的工質(zhì)，實(shí)驗(yàn)研究納米流體對(duì)重力熱管傳熱性能的影響。本課題以小型重力熱管作為研究對(duì)象，設(shè)計(jì)制作了多根熱管，考察納米流體濃度、充液率、熱管傾角，冷凝段的換熱條件對(duì)重力熱管傳熱效率的影響，通過(guò)分析計(jì)算對(duì)比了不同熱管之間的傳熱性能差異。
本實(shí)驗(yàn)中，熱管工質(zhì)有兩種：去離子水、TiO2納米流體。實(shí)驗(yàn)相關(guān)參數(shù)為：加熱功率從20W到180W，以熱流量每遞增20W作為一個(gè)工況；TiO2納米流體的濃度為0.2%wt、0.5%wt、1%wt、2%wt；重力熱管的充液率為50%、60%、70%；熱管傾角為豎直和水平；冷凝段換熱條件為自然空冷和強(qiáng)迫風(fēng)冷，風(fēng)速控制在6m/s。
實(shí)驗(yàn)結(jié)果表明，在采用納米流體作為工質(zhì)時(shí)，重力熱管的換熱性能有了較大幅度的提高，換熱系數(shù)比去離子水熱管最大增加了2.3倍。重力熱管換熱性能先隨納米流體濃度的增加而增加，而后隨濃度的增大而下降，這說(shuō)明對(duì)于重力熱管的換熱性能，納米流體存在一個(gè)最佳濃度。在本實(shí)驗(yàn)條件下，工質(zhì)為TiO2納米流體時(shí)，此最佳濃度在0.5％wt左右。當(dāng)充液率大于50%以后，納米流體重力熱管的換熱系數(shù)隨充液率的增大而快速下降，當(dāng)充液率達(dá)到70%，換熱系數(shù)僅為50%充液率的27.3%～40%，換熱性能惡化。在熱管的冷凝端加強(qiáng)制對(duì)流循環(huán)可以明顯降低冷凝段的溫度和熱管的工作溫度。
實(shí)驗(yàn)研究表明，以納米流體作為工質(zhì)，能夠顯著提高重力熱管的換熱系數(shù)，強(qiáng)化熱管的換熱性能。納米流體很有希望成為一種強(qiáng)化熱管換熱性能的新型工質(zhì)。

關(guān)鍵詞 納米流體；重力熱管；強(qiáng)化換熱；充液率


Abstract
With heat pipe being widely used in production and living areas, it’s more and more in-depth research. Many methods have been adopted to improve thermal performance of heat pipe. In recent years, nanotechnology are developed rapidly and applied in heat transfer enhancement. Therefore, it’s practical in theory that research new types of heat pipe combining nanofluid with heat pipe technology.
The author employed nanofluid as the working fluid in the gravity heat pipe. The experiments were carried out to explore the heat transfer enhancement of gravity heat pipe with nanofluid in it. In this study, a variety of heat pipes are produced. Effects of the TiO2 nanofluid concentration, filling ratio, inclination angle, thermal performance of condensation section on the efficiency of heat pipe were researched experimentally. The thermal performance of different gravity heat pipes was compared through the analysis and calculation after experiment.
The working fluids used in this experiment were DI water, TiO2 nanofluid. Parameters in this experiment were as follows: heating power increased from 40W to 80W, each increment of 20W as one working condition; the concentrations of TiO2 nanofluid were 0.2%wt, 0.5%wt, 1.0%wt, 2.0%wt; the filling ratios of heat pipe were 50%, 60%, 70%; inclination angles were vertical and horizontal; condensation section was forced air cooling with wind speed of 6m/s approximately.
The experimental results showed that the thermal performance of gravity heat pipe was greatly improved after nanofluid was used. Heat transfer coefficient increased by 2.3 times than heat pipe using DI water. The thermal performance of gravity heat pipe increased with increase of the particle concentration firstly and then decreased apparently which indicated that an optimal particle concentration existed. The optimal concentration of TiO2 nanofluid was about 0.5%wt in this experimental condition. After filling ratio is more than 50%, the heat transfer coefficient of gravity heat pipe dropped quickly along with the increase of filling ratio. Compared to 50% filling ratio, the heat transfer coefficient is only 27.3%～40% when filling ratio reached 70%. The thermal performance of nanofluid heat pipe got worse. Forced convectional circulation in condensation section can reduce the operating temperature of heat pipe as well as the temperature of condensation section apparently.
Experiment showed that the nanofluid could increase the heat transfer coefficient and improve the thermal performance of gravity heat pipe significantly. Nanofluid was expected to be a new type of working fluid to enhance the thermal performance of heat pipe.
Keywords nanofluid; gravity heat pipe; heat transfer enhancement; filling ratio





目 錄

摘 要 I
Abstract III
第1章 緒 論 1
1.1 研究目的和意義 1
1.2 國(guó)內(nèi)外研究歷史及進(jìn)展 1
1.2.1 熱管的發(fā)展 1
1.2.2 熱管的應(yīng)用 3
1.3 本文的研究對(duì)象和方法 3
1.4 本論文所作的工作 4
第2章 重力熱管理論 5
2.1 重力熱管簡(jiǎn)介 5
2.2 重力熱管的傳熱機(jī)理 6
2.3 重力熱管的傳熱極限 8
2.3.1 攜帶極限 8
2.3.2 沸騰極限 8
2.3.3 干涸極限 9
2.4 充液量與傾角對(duì)重力熱管傳熱的影響 10
2.4.1 充液量的影響 10
2.4.2 傾角的影響 11
2.5 本章小結(jié) 11
第3章 納米流體及在傳熱學(xué)中的應(yīng)用 12
3.1 納米流體簡(jiǎn)介 12
3.2 納米流體的制備 12
3.3 納米技術(shù)在傳熱學(xué)中的應(yīng)用 14
3.3.1 納米流體強(qiáng)化傳熱機(jī)理 14
3.3.2 納米流體在沸騰換熱中的應(yīng)用 14
3.3.3 納米流..