【作者】 于东；

【导师】 唐大伟； 胡学功；

【作者基本信息】 中国科学院研究生院（工程热物理研究所） ， 热能工程， 2014， 博士

【摘要】 微尺度传热是当今传热传质领域研究的重点,基于微尺度传热原理所设计的新型冷却方式已经广泛用于大功率电力电子设备元器件、中低温余热利用、大功率激光器冷却以及LED设备的冷却中。开放式毛细微槽群复合相变换热是微尺度传热领域中的一种,其相变换热的原理是液体在微槽群自身的结构所形成的毛细压力梯度下流动,在扩展弯月面区域形成具有高强度蒸发能力的薄液膜区域和厚液膜区域的核态沸腾的高强度复合相变换热。目前微槽群复合相变冷却方式已经得到国内外学者的广泛重视,进行了大量研究并取得了一些重要成果。本文利用Micro-PIV设备对硼硅玻璃材质的矩形毛细微槽群热沉内的弯月面的形状进行可视化实验研究。研究了矩形毛细微槽群热沉在纯蒸发换热状态下,水平放置、倾斜15°、25°和35°时,不同热流密度条件下,微槽群内轴向截面处自适应段、渐缩段和三角区域流动段的弯月面的形状沿轴向的变化情况,并对弯月面形状的实验数据进行拟合处理；对弯月面形状沿轴向分布进行了三维图的绘制；研究了不同热流密度以及不同倾斜角度条件下弯月面的曲率半径沿轴向的变化情况。结果表明：在有热流密度输入时,矩形毛细微槽群热沉内弯月面的形状呈近抛物线形,水平槽内弯月面形状沿轴向是不变的；热流密度的增加对弯月面形状改变有较大影响；水平微槽内弯月面的平均曲率沿轴向基本保持不变,倾斜的微槽内弯月面的平均曲率沿轴向增加；在相同热流密度和相同倾斜角的条件下,三角区域流动段的弯月面沿轴向方向上逐渐向槽的角落退缩。利用Micro-PIV技术对硼硅玻璃和紫铜为基体材料的矩形微槽群热沉内的液体的速度场以及液体流动形态进行了可视化研究,研究了自适应段、渐缩段和三角区域流动段的速度场以及液体的截面积的变化情况并进行了分析；研究了切向方向上截面的速度矢量分布；研究了微槽在不同倾斜角度下槽内液体的流动状态,验证了前人的假设。结果表明：微槽内液体在无外力驱动条件下仅靠毛细力驱动,液体的流速很低,流动状态为层流状态；薄液膜区域的流速要远小于厚液膜区域的流速；矩形毛细微槽群热沉内的液体的流动状态验证了槽内存在自适应段和三角区域流动段；液体与微槽侧壁和槽底所围成的截面积沿轴向方向减小；自适应段和渐缩段的液体截面积拟合的结果为截面积沿轴向呈二次曲线分布；倾斜角越大,数据拟合的曲线的曲率越大,液体的截面积变化也越大；在相同轴向截面处液体的截面积随着倾斜角的增大而减小。三角区域流动段的液体的截面积沿轴向呈线性分布,液体截面积逐渐减小。研究了纯蒸发状态下的倾斜矩形毛细微槽内液体的流动特性并进行公式推导。根据前人提出的微槽内液体的轴向流动特性的理论模型进行修正,并与实验测量到的液膜厚度、曲率半径以及自适应段和渐缩段液体的润湿长度等实验数据进行对比,从而揭示矩形毛细微槽内弯月面的液体的液膜特性。利用高速摄影仪和红外热成像仪对饱和沸腾条件下矩形毛细微槽群热沉内汽泡动力学行为、三相接触线的波动时间以及微槽表面的温度分布等进行可视化实验研究,得到了汽泡破裂导致的三相接触线波动过程、不同热流密度条件下汽泡破裂导致的三相接触线形状的变化、热流密度对三相接触线的波动时间以及汽泡周期的影响、过热度对汽泡的脱离频率的影响、热流密度对汽泡破裂的当量直径的影响以及微槽温度表面的分布等规律。研究结果表明：汽泡的破裂使得三相接触线发生周期性的波动。随着热流密度的增大,接触线的振幅增大,波长变长,波动的更剧烈,接触线的波动传播的范围更广；接触线的波动时间随着热流密度的增加先增加后减小,存在一个峰值；汽泡的生命周期随着热流密度的增加而变短。汽泡破裂的当量直径随热流密度的增加而增大。在热流密度保持不变时,相同槽深条件下,汽泡的当量直径随槽宽的增加而增大；微槽群热沉表面的温度分布呈现波动趋势,存在温度的波峰值和波谷值；微槽表面平均温度随热流密度的升高而升高。汽泡破裂时汽化核心区域的温度在微槽表面3D温度分布图中出现波峰值。更多还原

【Abstract】 Microscale heat transfer is the main focus in the heat and mass transfer, and new cooling methods based on the microscale heat transfer have been widely utilized in high-power electronical components, low temperature waste heat utilization, high-power laser cooling and LED equipment. Combined phase-change heat transfer in open capillary microgrooves heat sinks is one kind of microscale heat transfer, and its principle of combined phase-change heat transfer in open capillary microgrooves heat sinks is driving fluid to flow along the axial direction of the microgrooves by capillary pressure difference due to the structure of the microgrooves, and forming thin liquid film where there exists high evaporating heat transfer coefficient and thick liquid film where nucleate boiling exists with high phase-change heat transfer coefficient. More attention has been paid to this new cooling method and more research has also been constructed and a lot of results have been achieved.In this work, visualization investigation of the meniscus shape in rectangular capillary microgrooves heat sinks with substrate material of borosilicate glass is conducted with Micro-PFV method. Investigations of the meniscus shape of accommodation, recession and corner flow stages in rectangular microgrooves heat sinks varying with axis under the condition of inclined angle of0,15degrees,25degrees and35degrees with different heat fluxes when the pure evaporation occurs in the rectangular capillary microgrooves heat sinks; data of the meniscus shape are fitted with parabolic curves, and3D profiles of the meniscus shape along the axis of the microgrooves are also attained. Curvature of the meniscus shape along axis of microgrooves is also investigated. Results show that the meniscus shape in rectangular microgrooves heat sinks is quasi-parabolic with heat flux added from below; the meniscus shape does not change along the axis in horizontal microgrooves; heat flux has great influence on the meniscus shape; the curvature of meniscus shape in horizontal microgrooves heat sinks does not vary along the axis, while the curvature of the meniscus shape in inclined microgrooves heat sinks increases along the axis; the meniscus shape of corner flow stage gradually recedes to the corner of the microgroove under the condition of the same heat flux and inclined angle.Visualization research on fluid velocity and flow patterns of rectangular microgrooves heat sinks with substrate material of borosilicate glass and red copper is constructed with Micro-PIV method. Velocity vectors and cross-section area of the liquid in accommodation, recession and corner flow stages are investigated; the velocity distribution in the tangential direction is also studied; flow patterns in different inclined angles are investigated and assumptions by Carton and Stroes have been confirmed. Results show that fluid in microgrooves driven only by capillary pressure difference flows very slowly and is under laminar flow; velocity in thin liquid film region is far less than that in thick liquid film region; the flow pattern confirms that there exist accommodation and corner flow stages; liquid cross-section area decreases along the axis; the fitted curves of the liquid cross-section area along the axis is a conic distribution; curvature of the curves increases with the inclined angle as well as the cross-section area; liquid cross-section area decreases with inclined angle in the same cross-section. The liquid cross-section area in corner flow stage along the axis is a linear distribution and cross-section decreases.The flow characteristics in inclined rectangular microgrooves heat sinks under pure evaporation condition are investigated theoretically, and the axial flow model in rectangular microgrooves heat sinks is revised. The analytical results are compared with the experimental results, such as thickness of the liquid film of the meniscus, curvature and the liquid length of accommodation stage and recession stage, and the liquid film characteristics of the meniscus are derived.Bubble dynamic behaviors and fluctuation of triple-phase contact line and the temperature distribution on the microgrooves are investigated by high speed camera and thermal infrared imager. The fluctuation of the triple-phase contact line caused by bubble-burst, the change of the shape of triple-phase contact line due to bubble-burst under different heat flux, impact of heat flux on fluctuation time of triple-phase contact line, bubble period, bubble-burst equivalent diameter and temperature distribution, influence of superheat on bubble departure frequency are all investigated. Results show that bubble-burst makes triple-phase contact line fluctuate periodically; with increase of the heat flux, the amplitude of the triple-phase contact line increases and wavelength elongates, so fluctuation becomes violent and the fluctuation region gets wider; fluctuation time first increases and then decreases, and there exists a peak value; the bubble period decreases with heat flux; bubble-burst equivalent diameter increases with heat flux; bubble-burst equivalent diameter increases with the microgroove width under the condition of the same heat flux and microgroove depth; temperature of the surface of the microgrooves heat sinks shows a trend of fluctuation, and there exist peak and trough values; the mean temperature of the surface of the microgrooves increases with heat flux; temperature of the region of the bubble-burst shows a peak value in nucleate site in3D temperature profiles.更多还原