闭合回路微通道中热驱动气液两相脉动流动行为及传热机理研究

Thermally driven vapor-liquid two-phase pulsation in closed-loop microchannel is a key thermophysical process involved in micro pulsating heat pipe, lab on a chip, microreactor, micro thermal control device, etc. The project will fabricate silicon microchips including closed-loop microchannels integrated with micro sensors by MEMS micromachining. The visualization experimental investigation on the thermally driven vapor-liquid two-phase pulsating behaviors and dynamic evolution of the flow regime will be conducted in the microchips via high speed microscope camera. The instability of vapor-liquid two-phase flow as well as heat transfer performance of the microchips will also be measured. The project is proposing to develop a 3D theoretical model of thermally driven vapor-liquid two-phase flow in closed-loop microchannel with a consideration of flow patterns evolutions and coupled evaporation/boiling, condensation and heat conduction. The coupled thermodynamics and kinetics mechanisms of thermally driven vapor-liquid two-phase flow and heat transfer are explored and analyzed. Especially, the influence of scale effect, interface effect and wall effect on thermally driven vapor-liquid two-phase pulsating behaviors as well as the mechanisms for start-up and instability of vapor-liquid two-phase pulsation will be elucidated. In addition, the structural optimization of vapor-liquid two-phase pulsating heat transfer microchannel array will be performed. This project is of significant scientific value in the exploration of microscale two-phase flow and heat transfer theory and will provide theoretical bases for the development of MEMS phase change heat exchangers.

闭合回路微通道中热驱动气液两相脉动流动是微脉动热管、芯片实验室、微反应器和空间微型热控制器等微系统中的关键热物理过程。本项目将基于MEMS工艺研制集成有微传感器的热驱动气液两相脉动流动闭合回路微通道换热芯片，采用高速显微成像系统开展微通道内热驱动气液两相脉动行为及流型动态演化的可视化实验研究，并测试气液两相流不稳定性及换热性能；建立考虑气液两相流型演化、蒸发/沸腾-凝结-导热耦合传热的微通道内热驱动气液两相脉动流动的三维理论模型并进行数值模拟；探析微通道内热驱动气液两相脉动流动及传热过程的热力学与动力学耦合作用机制，重点阐明尺度效应、界面效应和壁面效应对气液两相脉动流动行为的影响规律，揭示两相脉动流动的启动与失稳机理，开展热驱动气液两相脉动流动换热微通道结构的优化设计。本研究不仅对完善微尺度气液两相流动与传热基础理论具有重要的科学意义，也将为MEMS相变换热器技术的发展提供有力的理论支撑。

闭合回路微通道中热驱动气液两相脉动流动是微脉动热管、芯片实验室、微反应器和空间微型热控制器等微系统中的关键热物理问题。为此，本项目采用MEMS工艺研制了闭合回路微/小通道脉动热管可视化样件，开展了其内部热驱动气液两相脉动流动行为与传热特性的实验研究，建立了考虑气液两相流型演化、蒸发/沸腾-凝结-导热耦合传热的热驱动气液两相流动与传热的三维理论模型并进行数值模拟，阐明了尺度效应、壁面效应等对热驱动气液两相流动行为及传热性能的影响规律，提出了热驱动气液两相流启动特性的定量评估方法，掌握了热驱动气液两相启动与稳定运行的工况区间，揭示了热驱动气液两相流动与蒸发/沸腾-冷凝相变传热的耦合机理，实现了脉动热管闭合回路微小通道结构的优化设计。.研究结果表明：(1)脉动热管闭合回路微小通道中热驱动气液两相脉动流动行为包括四类要素：停滞、小幅脉动、大幅脉动和循环，其中，后两种流动行为下强制对流蒸发/沸腾-冷凝相变传热与强制对流显热传热共同作用，产生稳定高效的能质输运；通道尺寸减小将导致核态沸腾受限、丝状流与喷射流等特征流型产生、循环流动逐渐消失、能质输运效率与稳定性下降；(2)热驱动气液两相启动可分为突然式和渐进式两类模式，其动态特性可分别比拟为二阶欠阻尼动力学系统和一阶动力学系统的单位阶跃动态响应特性；充注有高饱和压力/饱和温度梯度工质的脉动热管具有良好启动性能；(3)热驱动气液两相脉动与循环行为分别呈现出低维和高维弱混沌特性，其产生的温度脉动信号的AR功率谱密度曲线和三维混沌吸引子形态可成为辨识两相流动行为特征的有效工具；(4)通道内引入微肋单元与周期性渐缩渐扩结构将产生流阻升高与流场扰动增强两种竞争效果，高热负荷下流场扰动增强效果占优，两类结构将强化气液两相脉动传热。.本项目的研究不仅对于完善微尺度传热传质基础理论具有重要的科学意义，也将为自驱动型气液两相变微换热器的研制及设计优化提供关键技术支撑。基于本项目研究成果，共在国内外期刊发表论文18篇（含2篇已录用），其中SCI论文12篇、EI论文6篇(不含SCI、EI双收录)；申请发明专利3件（其中已授权1件）；培养研究生5名。项目组负责人获评2017年江苏省“双创计划”科技副总。