超声波激励下脉动热管的启动特性及多场耦合强化的机理研究

Pulsating heat pipe has specific advantage on the utilization and transmission of waste energy. The theoretical analysis, numerical simulation and experimental test are combined to investigate evolution mechanism of nonlinear startup oscillation behavior and characteristics between the oscillatory flow and the heat transfer in pulsating heat pipe with multi-coupling fields. .In the theoretical region, physical model of pulsating heat pipe with unsteady oscillatory flow is developed based on self-organizing theory. The nonlinear startup evolvement process is deduced for pulsating heat pipe. The spatial and temporal distribution and variation of the multi-physical fields will be exhibited in the pipe. The nonlinear startup evolution mechanism of vibration in pulsating heat pipe will be revealed based on the above analysis..In the simulation region, numerical model according to the operating characteristics of pulsating heat pipe is built. The numerical algorithm of multi-physics, fluid-solid coupling, non-equilibrium is developed for pulsating heat pipe. The evolution process of startup characteristics will be displayed and the influence of cavitation effect on the vibration performance will be presented. .In the experimental region, the visualization experiment about oscillatory flow fields are tested by the field testing techniques in pulsating heat pipe. The change process of microbubble flow in heat pipe was analysed under ultrasound effect. The enhancement mechanism of heat transfer in oscillatory flow will be revealed under the ultrasound effect. Thus the design guidelines and improved technology will be proposed for better performance of pulsating heat pipe under the ultrasound. This project has wide application background as well as significant academic value.

脉动热管在余热利用与传递方面具有独特优势。项目通过理论分析、数值模拟与实验研究相结合的方式来揭示超声波激励下脉动热管非线性自组织启动机理与多场耦合作用下振荡流动换热特性。理论方面：基于自组织理论，建立非稳态脉动热管振荡流动物理模型，推导脉动热管非线性启动的演变过程，获得脉动热管内多物理场的时空分布和变化规律，揭示超声波激励下脉动热管自激启动的演变机理。数值仿真方面：建立针对脉动热管运行特性的数值模型，解决多物理场、流固耦合、非稳态脉动热管的数值计算问题，得到超声波激励下脉动热管非稳态启动演变过程，揭示空化效应对脉动热管启动性能的影响。实验方面：用可视化技术测得管内振荡流动形态，分析超声波作用下热管内微气泡流发生变化过程，揭示超声波激励下脉动热管内振荡流动与强化换热机理，为提高多场耦合下脉动热管性能提供设计依据和改进方向。该项目不仅具有较广的基础研究应用背景，而且具有重要的学术价值。

脉动热管在高热流密度传递与能量综合利用方面具有独特优势。作为一种特殊形式的热管，脉动热管集显热传递、潜热传递、局部脉动和整体流动以及热能与机械能的转换于一体的涉及多学科、多参数的汽-液两相流系统。超声波作为一种有源强化传热技术，主要作用机制是声空化作用。脉动热管内复杂的两相振荡流动换热过程与声空化外场的相互作用具有随机性，超声波激励脉动热管的传热特性取决于二者之间耦合作用的综合效果。因此，本项目开展了超声波激励下脉动热管启动特性及多物理场耦合作用下运行性能的研究。主要包括：(1)通过相变过程的分析和空化现象的模拟揭示了超声波对空化气泡的影响,给出了空化气泡在超声波作用下不断拉伸和压缩的微观机理，并提出缩聚链式反应的空化机理；(2)基于脉动热管的对称性，建立了二维数值计算模型，提出了不同结构的脉动热管优化方式。结果显示锯齿波纹结构位于冷凝段时，换热效率最高，增进了工质在冷凝段的相变量和液体工质量，弥补工质重力不足的缺陷，加快工质的回流，并且具有45°倾斜角连通路径的脉动热管的冷凝效果比传统的脉动热管好；(3)实验探究了施加超声波前后去离子水脉动热管的启动特性和换热性能的变化，在低加热功率下加入超声波，有利于脉动热管启动。探究了超声波对纳米流体工质的气液两相流动和传热性能的影响，揭示了纳米流体与超声波复合强化传热的机理。本项目的研究结果对于拓展脉动热管的应用范围、提升热管系统的能量传递效率具有重要的科学意义和工程应用价值。