多因素耦合条件下微通道沸腾不稳定触发机制及模式识别

Recently, microchannel flow boiling heat transfer provides an alternative and potential way for thermal management of high-power electronic chips. And the effect of microchannel boiling instability on boiling heat transfer becomes the primary restriction problem to maintain the excellent performance and stability of the microelectronic device. Although appreciable research efforts have been forced on microchannel boiling instabilities, most of the existing work has been experimental demonstrations and visualization. Only a few physical and mathematical research have been reported in the open literature on the triggering mechanism and mode identify for boiling instability under multifactor coupling conditions. This project proposes a new scientific concept of establishing unified criteria for boiling instability-triggered mechanism by quantitative analysis methods. Considering the effect of nucleation on the wall, compressible volume, and rapid bubble growth on the boiling instability, the corresponding lumped dynamic flow and heat transfer nonlinear model with dominant triggering mechanism for the two-phase boiling instability system is proposed. And the mathematical analysis method for the theoretical model is established to achieve the judgment criteria for boiling instability-triggered mechanism quantitatively. The silicon microchannel heat sink with trapezoid cross section is designed as the experimental section, and the experimental verification is performed, then the fine improvement for the model can be implemented in accordance with the experimental results. In addition, with the discrete wavelet decomposition analysis method, the coupled fluctuation wave signals in the experiment is decomposed to identify the various oscillation modes. Finally, with the unified dimensionless criterion, the project can propose the dominant triggering mechanism and identified modes for microchannel boiling instaility.

微通道沸腾换热成为高功率电子芯片冷却热管理极具潜力的选择，而微通道沸腾不稳定对沸腾换热影响是主要制约问题。目前研究大都基于实验进行沸腾不稳定现象观察，鲜少对多因素耦合条件下不稳定触发机制及其模式展开机理讨论。本项目提出从定量分析角度建立微通道沸腾不稳定触发机制判断准则的科学构想。围绕“不同沸腾不稳定占优触发机制及模式识别”这一核心科学问题，考虑壁面核化、可压缩容积，及汽泡快速生长对沸腾不稳定影响，构建微通道沸腾不稳定不同占优触发机制下系统级集总动力学流动-传热非线性理论模型；建立理论模型数学解析方法，获取沸腾不稳定触发机制定量判断准则；设计微通道热沉并进行实验验证，依据实验结果精细刻画理论模型结构。建立离散小波时域和频域分析方法，解耦分层实验不稳定波动信号，获取沸腾不稳定模式判别。研究结果获取统一无因次准则数下不同沸腾不稳定占优触发机制及其模式识别，掌握沸腾不稳定基本物理特征。

微尺度流动沸腾传热在实际应用过程中，常伴随着沸腾不稳定，严重阻碍微电子系统的正常运转。因此有必要对微尺度流动沸腾不稳定展开进一步研究。研究内容主要从三个方面展开：①梯级多孔肋壁效应实验研究；②基于稳定性判别准则数下梯级多孔肋壁微通流动沸腾不稳定分类；③建立时域和频域分析方法对沸腾不稳定数据信号进行解耦分层。研究结果表明：（1）首次获得了多孔肋壁互联互通效应下单个核化汽泡可在2ms内触发整个微通道核化沸腾，以及多孔肋壁效应下的肋壁间毛细力效应供液对抑制局部干涸从而有效抑制沸腾不稳定的现象；（2）以G/q作为稳定性判别准则，梯级多孔肋壁微通道流动沸腾在q-G二元坐标图上可分成五种沸腾模式，首次发现半稳定汽液两相流动沸腾模式。（3）建立DWT耦合PSD分析方法对沸腾不稳定数据信号进行解耦分层，发现毫秒级流型转换主导下的次波动模式，首次发现了中心带液条环状流，此流型可在一定程度上延缓蒸干的出现，从而从根本上抑制流动沸腾不稳定。本课题研究成果有助于从机理上掌握微纳尺度下流动沸腾不稳定的触发机制，可为从源头抑制并消除微纳尺度流动沸腾不稳定提供参考。