超高速微电主轴纳米流体热管高效散热机制研究

Based on the thermal behavior and heat dissipation requirements of ultra-high-speed micromachining motorized spindles, a novel type of highly efficient heat transfer component, miniature rotating heat pipes using nanofluid as working fluid, is firstly proposed to effectively cool the bearing-rotor system in this project. It is planned to reach the goals of the proposed project by combining the experimental investigation, theoretical and numerical analysis. The nanofluid liquid film distribution, vapor-liquid interface evolution and nanoparticle migration under the coupling effect of microscale effect and centrifugal force in the heat pipes will be studied to reveal the phase-change heat transfer and flow characteristics of nanofluid in miniature rotating heat pipes. The start-up characteristics, heat transfer capacity and heat transfer limits of heat pipes will be comprehensively analyzed for different operating conditions, different working fluids and heat pipe structural parameters to obtain the effect of coupling multiple factors on heat transfer performance of nanofluid heat pipes. Based on the study of the flow and heat transfer mechanism, to develop a reasonable nanofluid heat pipes optimization model and multi-objective optimization method for the design of high-efficiency cooling of ultra-high-speed micromachining motorized spindles. A micromachining motorized spindles prototype using heat pipes cooling the bearing-rotor system will be designed and manufactured to verify its engineering principles, and its thermal characteristics will be tested to clarify the effect of heat pipe on temperature and thermal deformation of the micromachining motorized spindles. The research results of this project will provide a new theoretical basis and design method for the temperature control of the rotating hot parts of micromachining motorized spindles.

本课题针对超高速微电主轴的热特性和散热需求，提出用纳米流体微小旋转热管这一新型高效传热元件冷却轴承-转子系统。拟采用实验、理论分析和数值模拟相结合的方法，研究微小尺度效应与离心力耦合作用下热管内纳米流体液膜分布、汽液界面演化和纳米粒子迁移等问题，进而揭示微小旋转热管内纳米流体流动与相变换热特性；系统分析不同运行工况、不同工质和热管结构参数组合条件下的热管启动特性、传热能力和传热极限，获得耦合多因素对纳米流体热管传热性能的影响规律；在流动传热机理研究的基础上，凝练合理的优化模型，构建适合超高速微电主轴高效冷却要求的纳米流体热管多目标优化方法；设计实现基于轴承-转子系统热管冷却的微电主轴原型，并对其开展热特性实验研究，阐明热管对微电主轴温升和热变形等的影响规律，完成超高速微电主轴热管散热的工程原理验证。本项目研究成果将为微电主轴旋转热部件的温度控制提供新的理论依据及设计方法。

针对超高速微电主轴的热特性和散热需求，本项目提出用纳米流体微小旋转热管这一新型高效传热元件冷却轴承-转子系统。深入研究了超高速微电主轴纳米流体热管高效散热机制，为微电主轴旋转热部件的温度控制提供新的理论依据及设计方法。本项目的研究内容、重要结果主要包括：1）对旋转状态下纳米颗粒迁移对薄液膜相变传热和液滴成核的影响进行了分析；建立了三维纳米流体旋转热管分析模型和数值计算方法，以及微电主轴热-结构耦合特性分析方法，并用实验数据进行了校核验证。2）进行了冷却高速电主轴轴承-转子系统的热管流动换热机理可视化实验，分析了热管的启动特性和气液两相流动特性，发现由于工质过冷和界面汽化热阱导致的蒸发段温度过冲现象。3）通过数值模拟和实验研究，分析了转速、充液率，纳米颗粒体积分数和粗糙度等对微小旋转热管流动和传热特性的影响规律，以及适合超高速微电主轴高效冷却要求的热管优化方法。稳态时热管内壁面处形成环状流，离心力的作用使气化核心无法长大形成大气泡，而是以直径很小的微气泡集群形式脱离壁面。纳米颗粒加剧了气液两相的相互作用，提高两相传热传质速率。 0.01%wt的ZrO_2纳米颗粒可降低热管热阻约12%，但热阻的减小幅度随着纳米颗粒质量分数的增大而降低。转速增大可减小蒸发段液膜厚度，并增强冷凝段回流效率，从而降低热管热阻。转速从 6000rmp 增大至 12000rmp 时，热阻降低约7.5%。4）设计了环路热虹吸旋转热管和平行轴旋转热管这两种不同结构旋转热管冷却电主轴，并开展热特性数值和实验研究，阐明了热管对微电主轴温升和热变形等的影响规律。环路热虹吸管电主轴冷却结构，在5000~20000r•min-1的范围内，使电机转子温度降低13~32%，转轴温度降低19~28%。平行轴旋转热管冷却电主轴，轴芯最高温升减少34%，轴承最高温升减少35.6%；电主轴前端中心点轴向热变形由5.6μm减小至4.5μm，减小了19.6%。轴芯冷却使轴承预紧力和轴承支撑刚度，以及主轴一阶固有频率均降低。改善电主轴热特性的同时，保证系统有良好的机械特性。