窄微多通道流动不稳定性的气泡动力学触发机制

Two-phase flow instability may be occurred in thermal systems which are composed by micro- and mini- multichannel; it will affect its efficiency and thermal security. The mechanism of the flow instability is closely relating to the evolution of bubbles in the flow channel and its localization properties. To control the occurrence of the flow instability, it is an important way to improve the performance of thermal equipments involving the mini- and micro- multichannel such as electronic cooling, moveable nuclear reactor, evaporator of automotive air conditioner and MEMS (MicroElectroMechanical Systems) technology. This project will combine the experimental study and theoretical analysis, and the automatic bubble nucleation technology to study the basic phenomena of the flow instability in micro- and mini- multichannel, to probe the physical triggering mechanism of the instability from the views of bubble dynamics and the local interface behavior characteristics. At the light of the serious wall effects and interface effects, we also want to determine the occurrence of boundary threshold and the criteria of the two phase flow instability of mini- and micro- multichannel at the view of bubbles evolution. At the abovementioned fundamental understandings, the instability control methodology would be initially considered through the comprehensive methods of geometry, wall characteristics, the second energy interference and other mechanisms based on density wave instability. This project will focus on the evolution of the local bubble effects on the flow instability, and probe its triggering mechanism, the above content have not yet published on the international references so far.

由窄微多通道所构成的热系统中，流动沸腾会引起温度和压强的波动。这种流动不稳定性会导致系统效率降低，并可能因阻液和烧干而导致元件烧毁。该流动不稳定性的触发机制与空泡演化和局域特性密切相关，控制流动不稳定性的发生是利用窄微流道作为元件的相关热设备提高性能的一个重要方面，如电子冷却、汽车空调换热元件、MEMS器件、可移动核反应堆等应用中那样。本项目拟结合可视化实验、理论分析及可自动核化的气泡动力学模拟技术，从气泡动力学特性、流动结构及局域界面特性找到触发流动不稳定性的动力学机制，从空泡演化及流场结构驱动角度来确定界面效应和严重壁面效应综合作用下的窄微多通道系统内流动不稳定性发生的阈值和判据，并初步综合考虑几何形状、壁面特性、第二能量干扰和其它基于密度波的流动不稳定抑制方法。本项目着眼于局域空泡演化及相间界面作用对流动不稳定性的影响，探讨其触发机制，以上内容在国际上还未见相应文献发表。

项目采用可视化实验、理论分析和数值模拟相结合的方法，对窄微多通道内的流动不稳定性的气泡动力学触发机制进行了系统深入的研究，完成了项目计划书规定的各项研究内容，实现了预期目标。项目主要研究内容和研究成果如下：. (1)搭建了窄微多通道流动沸腾综合实验平台。基于该平台，测量和研究了窄微多通道流动不稳定性发生的宏观参数特性，分别观察了窄微多通道系统内流动不稳定性的发生条件和表象，并通过高速摄像了解部分局域流场特征。分析了不同实验工况对流动不稳定性触发的影响，开展了平行矩形微通道内局部和整体压降特性的研究，总结及讨论了关于窄微多流道流动不稳定性的物理机制及振动特性，并开发了可测量微液膜的微型传感器矩阵。该部分工作为理论分析和数值模拟提供了基础。. (2)基于Kevin-Helmholtz 流动不稳定性，对小通道内环状流汽液界面进行了理论研究，提出了液膜厚度以及剪切扰动波波动特性的相关模型。同时从理论上完成了微通道内基于汽核倒流的压力波动模型，完成了对微通道内汽核核化、生成拉长、汽核倒流与微通道重新润湿的整个高振幅低频率流动不稳定性过程的预测。并从汽泡动力学特性、热工参数、流体物性参数和流动结构等方面对流动沸腾不稳定性的影响展开了研究。. (3)基于分子动力理论，考虑界面处界面蒸发/冷凝因素以及汽泡底部微液层传热因素建立综合传热传质相变模型，实现了对窄通道内汽泡的演化过程的成功模拟和自动核化的汽泡动力学模拟技术的完善。. 本项目目前已在国内外核心期刊等发表研究论文26篇，其中SCI收录12篇，EI收录7篇；国际会议收录7篇，国内会议3篇，已培养硕士8名，博士2名，博士研究生2名。