【作者】 许佳寅；

【导师】 徐宏； 张莉；

【作者基本信息】 华东理工大学 ， 动力工程及工程热物理， 2013， 博士

【摘要】 铜-水LHP同时发挥了铜吸液芯的高效蒸发和水汽化潜热高的特性,是一种具有理想组合的高效两相被动式传热元件,在大功率电子芯片和LED的冷却领域具有重要的应用潜力。传统结构的铜吸液芯蒸发器因热泄漏较为严重,启动速率低,大幅度降低其传热性能,影响了LHP的推广应用。本文以抑制铜-水LHP的热泄漏与提高蒸发器的性能为目标,主要研究内容及创新成果如下：(1)采用吸液芯与蒸发器壳体一体化烧结方法,提出了无蒸汽回流圆柱形蒸发器,消除了接触热阻和高功率运行时蒸汽回流到储液槽的可能性。实验证明该新型蒸发器启动过热度低、响应速率快,运行时蒸汽不再回流至储液槽,系统的稳定性、可靠性显著提高。(2)采用全透明蒸发器实现了平板型铜-水LHP蒸发区域、吸液芯和储液槽的可视化。研究发现,低功率启动初期,在铜吸液芯上表面因热泄漏生成了气泡,启动较为缓慢；高功率运行时,储液槽内出现的内热管效应。(3)实验与数值模拟相结合,研究了铜粉平均颗粒直径对烧结型吸液芯蒸发器传热性能的影响。探讨了吸液芯平均孔径对蒸发器热泄漏和LHP启动特性的影响。分析了稳态运行时不同加热功率下铜粉平均颗粒直径对蒸发器内汽液两相分布、传热效率、蒸汽排出速度的影响规律,发现铜-水LHP的热泄漏对粉末平均颗粒直径的变化较为敏感。实验采用的三种不同铜粉颗粒中,当铜粉平均颗粒直径为139.2μm时,LHP低功率下启动速度较快、稳态运行时极限功率可达500W,同时具有良好的启动和运行特性。(4)研究了充液率对铜-水LHP综合传热特性的影响,采用高速摄影技术对平板型LHP蒸发器进行液体循环可视化实验研究。实验发现,铜-水LHP蒸发器在充液率较低时干涸和湿润交替出现,导致运行温度波动剧烈。高充液率对热泄漏有明显的抑制作用,能够提升启动速率和极限加热功率。充液率为69.6%至78.3%的圆柱形LHP的综合性能最佳。(5)为了减小铜-水LHP在低功率启动和高功率运行时出现的热泄漏,在吸液芯中引入导热系数较低的金属粉末材料,开发成功铜镍双层烧结型吸液芯蒸发器。优化获得了铜、镍层的最佳厚度比为3：2,该新型吸液芯同时具有高效蒸发和抑制热泄漏的优点。采用实验和数值模拟相结合的方法,研究了铜镍双层吸液芯对热泄漏的抑制效果及其机理。实验结果表明,铜镍双层吸液芯中的镍层能够避免启动初期吸液芯上表面气泡的生成,加快了启动速率,启动耗时减少37.7%；高加热功率运行时(120W),储液槽内部不再产生内热管效应,运行中蒸发器的壁面温度降低约10℃。更多还原

【Abstract】 Copper-water LHP can simultaneously present the highly efficient evaporation of the copper wick and high latent heat of water vaporization. Therefore, it is an effective two-phase heat transfer device, which features a passive heat transport system without moving parts. LHP has promising prospects in applications such as the cooling of high-power electronic chips and Light-Emitting Diodes (LEDs). However, massive heat leak resulted from traditional evaporator with a copper wick leads to a slow start-up process, poor heat transfer performance, which limits the application in electronic thermal management.In this paper, researches on evaporation enhancement and heat leak alleviation in the copper-water LHP were carried out. Main works and results are as follows:(1) A cylindrical evaporator without vapor deprime, which characterizes the eliminations of the contact thermal resistance and the chance of vapor deprime, was proposed. It was experimentally testified that the cylindrical evaporator could achieve a fast start-up with a low superheat, avoid the appearance of vapor deprime at high heat load operation, and improve the stability and reliability of the LHP.(2) Within the evaporating zone, the wick and the compensation chamber of a flat LHP evaporator, visual observations of the flow were realized by a transparent evaporator cover. It was found that:1) some bubbles were accumulated on the upper surface of the wick during the incipient stage of the start-up process at low heat load, which resulted in a slow start-up process.2) Heat pipe effect was shown in the compensation chamber during the steady operation at high heat loads.(3) With the combination of experiment and numerical simulation, the effect of average particle diameter of the sintered copper wick on heat transfer was studied. The influences of average pore size on heat leak and start-up characteristics were also discussed. The effect of copper wick average particle diameter on the distribution of the two-phase in the evaporator, the efficiency of heat transfer and the velocity of the vapor flow were analyzed during the operation at different heat loads, which concluded that heat leak was sensitive to the average particle diameter of the powder. When the average particle diameter of the copper powder is139.2μm among three kinds powder, the LHP could reach a fast start-up, and the heat transfer capacity of500W was reached during the operation. (4) The effect of charging ratio on copper-water LHP heat transfer characteristics was investigated. Visualization research on working fluid circulation in flat LHP evaporator was also performed, taking advantage of high-speed camera. Due to low charging ratio, strong temperature oscillation resulted from the alternative appearance of dry up and wet in the flat evaporator was observed during operation. The experimental results demonstrated that obvious heat leak was alleviated by the high charging ratio, which generated in a fast start-up and a high heat transfer capacity. The optimal charging ratio for the cylindrical LHP ranged from69.6to78.3%.(5) In order to address massive heat leak in copper-water LHP during low heat load start-up and high heat load operation, nickel layer with low thermal conductivity was introduced to manufacture a new two-layer copper-nickel composite wick. When the thickness ratio of copper layer to nickel layer was3:2, efficient evaporation and low heat leak were achieved simultaneously at the same time. With the combination of experiment and numerical simulation, the mechanism of heat leak alleviation from the two-layer copper-nickel composite wick was also studied. It was found that nickel layer of the wick could prevent bubbles from creating on the upper surface of the wick during the incipient start-up process, speed up the start-up process and reduce the time for start-up process by37.7%. No heat pipe effect was shown in the compensation chamber during the operation at a high heat load of120W, and the evaporator wall temperature was about10℃lower than before.更多还原