【作者】 甘云华；

【导师】 徐进良；

【作者基本信息】 中国科学技术大学 ， 工程热物理， 2006， 博士

【摘要】 各种微系统的迅速发展，为微流体的流动与传热研究提出了迫切的要求。本文主要针对微流体在硅基微通道内的单相和汽液两相流动与传热进行了系统的实验研究。 本研究采用标准的微电子机械系统加工工艺，设计并加工了2种不同结构的硅基微通道实验段。一种为常规结构的并联硅基微通道，另一种为基于“热边界层再发展概念”设计出的新型结构的并联硅基微通道。这2种不同结构的硅基微通道的水力直径均为155.3微米，且具有可比性。建立了微流体光学平台，形成了一整套的微流体实验系统。 采用水和甲醇为工质，在常规结构硅基微通道内进行了单相强制对流换热实验研究。基于实验结果，得出了摩擦常数及努塞尔数的实验关联式。 在相近的工况下，以水为工质进行了新型结构微通道与常规结构微通道之间流动与传热特性的对比实验研究。结果表明采用新型结构能在强化传热的同时降低微通道进出口压差。 以丙酮为工质，在常规结构硅基微通道内进行了沸腾传热实验研究。所有微通道中均产生微时间尺度的瞬变流动，其瞬变流型的周期为毫秒量级。1个完整的周期可以分成3个子过程。观测到了4种不同的汽液两相流流型，统计分析显示这4种流型出现的概率满足统计规律。还观察到了“微汽泡爆炸现象”。 通过绘制壁面过热度及质量流速随热流密度的变化关系，鉴别出了沸腾起始点。根据观测到的瞬变流型，鉴别出了5种沸腾传热机制。 基于无量纲的沸腾数，将沸腾传热划分成了3个不同的区域，并给出了区域间的转换准则。不同的沸腾传热区域内起主导作用的沸腾传热机制是不同的，从而揭示了控制微尺度沸腾传热的统一规律。通过选取合适的沸腾数范围，可以获得均匀的壁面温度场。 在核态沸腾传热机制控制下，沸腾传热系数及壁面温度场仅与热流密度有关。基于核态沸腾传热实验结果，提出了2个不同形式的核态沸腾传热系数实验关联式，都能对本核态沸腾传热实验结果进行较好的预测。 在强制对流沸腾传热机制控制下，沸腾传热系数主要取决于质量流速，而受热流密度的影响较小。基于强制对流沸腾传热实验结果，提出了1个新的强制对流沸腾传热系数实验关联式。该实验关联式能对本强制对流沸腾传热实验结果进行很好的预测。更多还原

【Abstract】 Understanding the fundamentals of fluid flow and heat transfer of Microfluidics has become crucial for the rapid development of all kinds of Micro Systems. In this study, systematic experimental investigation was carried out on single-phase fluid flow and vapor-liquid two-phase flow heat transfer in silicon microchannels.Two silicon microchannel test sections were designed and fabricated using the standard Micro- Electro- Mechanical Systems techniques. One is the conventional parallel silicon microchannel test section; the other is the new parallel silicon microchannel test section which was designed based on the thermal boundary layer redeveloping concept. Both of the two types of microchannels have the same hydraulic diameters of 155.3 microns, and have comparability. A Microfluidics optic platform and an experimental system were set up.An experimental study of forced convective heat transfer through conventional microchannels was performed using the water and methanol as the working fluids. The experimental correlations of friction constant and Nusselt number were gained based on the experimental results.Using water as the working fluid, comparative experiments were carried out between the two test sections. And experimental results show that the new structure microchannels can enhance heat transfer and reduce pressure drop across microchannels at the same time.Boiling heat transfer experiments in conventional microchannels were performed using acetone as the working fluid. All microchannels display the transient flow pattern behavior in milliseconds. A full cycle can be subdivided into three stages. Four different vapor-liquid two-phase flow patterns were observed. The statistical analysis shows that the occurring probabilities of the four flow patterns satisfy the statistical principle for successive cycles. And the bubble explosive phenomenon was observed.By plotting the curves of wall superheat and mass flux versus heat flux, the boiling incipiencies were obtained. In terms of the observed transient flow patterns in microchannels, five heat transfer mechanisms are identified.Three different boiling heat transfer regions were divided by the non-dimensional boiling number, and the transition criteria among the three heat transfer regions are given. The dominant boiling heat transfer mechanisms are different in different boiling heat transfer regions, and the unified law that controls the microscale boiling heat transfer was discovered. A uniform chip temperature field could be acquired by selecting the suitable boiling number ranges.When the nucleate boiling heat transfer is dominant, both the boiling heat transfer coefficients and chip temperatures are dependent on the heat fluxes only. Two new correlations were put forward, which all can predict the nucleate boiling heat transfer results well.When the forced convective boiling heat transfer is dominant, the boiling heat transfer coefficients are mainly dependent on mass fluxes and less dependent on heat更多还原