纳米流体沸腾换热实验研究
本文选题:纳米流体 + 沸腾换热系数 ; 参考:《江苏科技大学》2017年硕士论文
【摘要】:近年来,电子器件体积日趋小型化和集成化,单位面积的热量集聚严重,由此引起的散热问题日益严俊,如何实现热量的高效传递以保证大功率电器的安全运行,一直困扰着相关领域的研究者。关于纳米流体汽液两相流强化传热方面的研究结论,在当今传热学领域仍存在较大争议;且由于它在实际应用中需求较大,促使各国相关领域研究者对其进行实验研究和理论分析,但大部分仅局限于理论研究方面,实验研究相对较少,因而本文希望通过实验研究的方法,探讨影响纳米流体沸腾换热性能的实验机理,为实现更高效率的强化传热作铺垫。本文在综述了目前国内外纳米流体沸腾换热的研究及其进展情况的基础上,对纳米流体进行了沸腾换热实验研究,探讨其中蕴含的传热机理,为进一步强化沸腾换热提供参考依据。首先采用两步法制备了不同组分的纳米流体,对其导热系数等物性参数的影响因素进行了理论分析。然后,精心设计并搭建了纳米流体沸腾换热的实验装置,并结合已有的且研究比较成熟的水的沸腾换热曲线,验证了实验装置的可靠性及可重复性。进而介绍了具体的实验方案及实验方法,对不同纳米流体的沸腾换热特性进行实验研究,利用高速摄像机对沸腾换热过程进行了可视化观测,记录沸腾蒸发腔内气泡变化规律及相关试验数据,并对沸腾换热前后加热铜柱的上壁面情况进行了SEM表征对比。通过实验数据、气泡图像、壁面形态等信息的整理,对比分析不同基液组分、纳米颗粒浓度、纳米颗粒粒径、纳米颗粒种类在不同系统运行压力下的沸腾换热特性的差异,进而分析以上各因素对纳米流体沸腾换热性能的影响及其作用机理。本文实验研究结果表明:(1)在低浓度范围内,纳米颗粒质量浓度越大,越有利于纳米流体沸腾换热性能的提高。纳米颗粒平均粒径为30nm,质量浓度分别为0.001%、0.005%、0.01%的水-氧化铝纳米流体的沸腾换热性能从左到右依次变大。(2)纳米流体的沸腾换热性能与纳米颗粒种类有关,在其他条件相同的情况下,纳米颗粒的物性,诸如导热系数、比热、密度、粘度等,均会影响纳米流体的沸腾换热性能。纳米颗粒平均粒径为30nm、质量浓度为0.005%的水-氧化铝纳米流体的沸腾换热性能比水-二氧化硅更好。(3)对于制备纳米流体的基液,也会影响纳米流体的沸腾换热性能。纳米颗粒平均粒径为30nm、质量浓度为0.005%的氧化铝纳米流体,混合基液中乙二醇的质量分数越低,纳米流体的沸腾换热性能越好。(4)在试验范围内,纳米颗粒的平均粒径越小,纳米流体的沸腾换热性能越好。质量浓度均为0.005%,平均粒径为30nm的水-氧化铝纳米流体的沸腾换热性能优于平均粒径为50nm的水-氧化铝纳米流体。(5)试验系统的工作压力对纳米流体的沸腾换热性能有重要影响。实验结果表明,与高压条件相比,纳米流体在低压条件下的沸腾换热性能更好。
[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.
【学位授予单位】:江苏科技大学
【学位级别】:硕士
【学位授予年份】:2017
【分类号】:TB383.1;TK124
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