受限空间内图形化碳纳米管阵列吸液芯中热流输运及蒸发/沸腾传热强化

Due to the relatively low heat transfer limit of various MEMS micro heat pipes featured with microchannel and micro-pin-fin wick structure, they are not competent to the current effective cooling of ultra-high heat flux generation from high-power electronic devices (represented by microelectronics chips). As to this problem, this research will give a strategic solution that using aligned carbon nanotube arrays characterized by ultra-high thermal conductivity as the novel wick. In this research, the patterned aligned carbon nanotube arrays with hierarchical micro/nano structure fabricated on the silicon wafer within confined space are used as the object of study. With the aid of experimentally visualization, intergrated heating and temperature measurement technology, and theoretically multiscale simulation approach, the effects of micro-pin-fin cross-section shape, height, arrangement and density on the capillary action and permeability of wick will be quantitatively analyzed. Then, mutual influence and relationship for fluid flow and heat transport between carbon nanotube bundles and micro-pin-fins will be discussed to clarify the mechanism that contributes to the significant increase of evaporation/boiling critical heat flux and heat transfer coefficient in confined space after using carbon nanotube arrays. Besides, in order to enhance the heat transfer limit and thermal management effectiveness of micro heat pipes, the effects of wick geometry parameter, arrangement and working fluid on its stable and reliable work under high heat flux will be discussed and analyzed. This research will lay a theoretical fundation for the applications of aligned carbon nanotube arrays wick in the fields of MEMS micro heat pipes (especially silicon heat pipes) as well as other micro-coolers for the cooling of high-heat-flux electronics.

针对以微槽道和微肋等结构为吸液芯的MEMS微型热管存在传热极限偏低、难以适应当今高发热器件（以微电子芯片为代表）冷却温控的问题，本研究提出将具有超高热导率的碳纳米管阵列作为新型吸液芯的解决方案。以受限空间内硅基表面图形化微/纳复合结构碳纳米管阵列作为研究对象，采用可视化观测、集成加热/测温和微/纳跨尺度模拟相结合的研究方法，定量解析吸液芯微肋截面形状、高度、排布方式和疏密程度等因素对其毛细作用和浸润渗透率的影响规律，探索碳纳米管管束与微肋间热流输运的相互作用关系，阐明碳纳米管阵列吸液芯对提高受限空间内蒸发/沸腾临界热流密度和相变传热系数的作用机理，揭示吸液芯几何结构参数、排布方式和工质种类对高热流状态下保持其稳定可靠工作的影响规律，以达到增强微型热管传热极限和温控能力的效果，为碳纳米管阵列吸液芯在高热流强度下MEMS微型热管（特别是硅基热管）和其它微型冷却器方面的应用推广奠定理论基础。

液滴撞击固体表面现象在材料科学、化学工程、动力机械等领域普遍存在，已成为微小液滴研究领域的重要方向。本项目借助实验和理论研究，重点开展了针对非图形化超疏水CNT阵列液滴撞击试验、表面润湿性改变的非图形化CNT阵列液滴撞击试验、微/纳复合结构图形化CNT阵列加热条件下的液滴撞击试验以及硅基亚微米硅柱阵列表面加热条件（200-550 ℃）下的液滴撞击试验。发现在液滴铺展阶段宜采用Kistle模型作为动态接触角边界条件，而Blake模型则适宜于液滴收缩阶段。当液滴运动韦伯数（We）介于1.5到121之间时，其无量纲接触时间大致相同，约等于2.9。液滴在表面疏水性增强的情况下更易发生破碎，静态接触角低于105°的表面随着We的增大液滴处于表面粘附状态且不再变化；当We增大时表面润湿性对接触角振荡变化影响不大，原来无序交错的CNT阵列可转变成近似蜂巢状结构，且由超疏水转变为亲水特征。对于微/纳复合结构图形化CNT阵列，可以显著抑制液滴碰撞过程中“视在Leidenfrost效应”的出现，较光滑硅片大约提高100℃，沸腾/蒸发散热能力有效提高。对于亚微米硅柱阵列，温度对相同We下液滴铺展因子影响不大，铺展过程受惯性力主导，与光滑表面相比可显著提高Leidenfrost温度；提出了液滴撞击高温亚微米硅柱阵列表面破碎弹跳机理，发现液滴破碎后主体脱离表面时间较未加热情况下更短，并给出了液滴主体部分与壁面接触时间的表达式。上述研究对认识常温/加热亚微米结构表面液滴撞击动态行为和过程特征提供了重要参考，对相关表面设计应用具有很好的指导意义。同时，首次将微槽道、烧结泡沫铜和烧结铜粉吸液芯结构分别引入管状脉动热管、平板槽道脉动热管和带平板蒸发器的三维脉动热管中，发现与传统无吸液芯脉动热管相比上述吸液芯结构的引入可提高脉动热管启动和传热性能，同时铜粉吸液芯结构所具有的毛细作用还可有效提升热管的传热极限，将为实现传热高效强化提供有益参考，在微电子/光电器件和动力电池冷却方面具有很好地应用前景。