【作者】 唐琼辉；

【导师】 徐进良；

【作者基本信息】 中国科学技术大学 ， 工程热物理， 2008， 博士

【摘要】 近年来自然科学和工程技术发展的一个重要趋势是朝微型化迈进,微器件尤其是微电子机械系统正被应用于各个新兴行业。在器件的微型化过程中,发现了诸多宏观流体力学和传热学难以解释的现象,这些现象称为微尺度效应,由于微器件中存在大量的传热和传质交换,因此微尺度热效应是微尺度效应的一个重要分支。本文在微流体控制的应用背景下,以微传感器、微执行器等微器件广泛采用的薄膜微加热器为对象,从如下三个角度探讨薄膜微加热器的微尺度效应与微气泡动力学现象:1.气泡产生前薄膜微加热器的温度场研究由于微尺度效应薄膜微加热器的温度具有与常规尺度下的加热器不同的温度场分布,而目前薄膜加热器上的温度主要根据加热膜的电阻-温度校正曲线,通过获取通过加热膜的电阻来间接测得薄膜加热器上的温度,而此温度为薄膜上的平均温度值。本文通过数学理论推导,获得了方形薄膜微加热器上温度的数学分析解,并据此得到了加热膜上的三维温度场分布。经过与现有的实验结果进行对比后证明此分析解符合物理实际。2.微气泡底层的薄液膜研究对薄膜微加热器表面加热后,所产生气泡与加热膜之间存在一层薄液膜.有关薄液膜方面主要集中在对管内产生的气弹和管壁之间的液膜研究,有关微加热膜表面受热后产生气泡和加热膜表面之间薄液膜的研究还比较少。本文在气泡动力学的基础上,通过数学分析,采用高阶runge-kutta方法对一定加热热流密度下的薄液膜进行了计算,并对所得结果进行分析,得到了较好的效果。3.强制对流条件下的微气泡动力学研究理解和认识微加热器上的汽泡动力学特性对于微流控系统中微汽泡执行器的设计和运行都具有重要的指导意义。目前,微加热器上的汽泡动力学特性研究仍是国际研究的前沿热点,而对强制对流条件下的微气泡动力学方面的研究比较欠缺。本文采用MEMS工艺,设计并制作了一种尺寸为^{100μm×20μm}的Pt薄膜微加热器,并置于硅通道内。对在液体工质的冲刷和脉冲加热条件下产生的气泡型态进行了分类,并研究了不同参数,如脉冲频率、占空比、液体工质流速等对微气泡动力学的影响;对脱离加热膜后通道内的气泡流型进行了分析;将微加热膜上的沸腾曲线与常规沸腾曲线进行对比,并对其异同进行了归纳总结。更多还原

【Abstract】 Devices Minimization is a new research field for sciences and engineering technologies.Micro devices such as MEMS are widely used in many industries. However,it is investigated that many phenomenon are difficult to be explained by regular physical mechanism,which are called microscale effects.Since great amount of heat and mass are transferred through micro devices,microscale heat transfer is critical for understanding the microscale effects.Since devices such as microsensors and microactuators use thin film microheaters as the heating-driven component,it has been studied by many researchers.In this paper,the investigation focuses on the following aspects:1.the temperature field of thin film microheater under pulse heating before bubble nucleationThe temperature field on a thin film microheater differs from that of a normal-sized film heater.Regularly the thin film temperature is indirectly measured, and it is often an averaged value.In chapter 2,an analytical solution is deduced for the temperature of the thin film microheater,thus the three dimensional temperature distribution is available.The analytical results are compared with the existed experimental values and are proved reasonable.2.The thin liquid film study under micro bubbleAs the thin film microheater is heated,bubbles are generated from above,and there is a thin liquid film between bubble and the microheater underneath.The existed studies mainly focus on the liquid film between vapor slug and the heated channel wall,and seldom is discussed on thin liquid film between heated surface and boiling bubble.A high order runge-kutta method is used to calculate the film thickness and under given heat flux,and the data were analyzed with good results.3.Micro bubble dynamics under forced convectionTo design a better microactuator in a microfluidic system,it is important to understand the bubble dynamics on the microheaters.At present micro bubble dynamics under forced convection is not fully studied.Based on MEMS technology,a platinum film microheater fabricated with the size of 100μm×20μm×10nm is placed in the silicon channel.With working liquid flowing through the pulse heated microheater,the bubble patterns generated are classified,and the effect of parameters such as pulse frequency f,τ₁/τ_cycle as well as the working liquid flow rate on micro bubble dynamics is discussed.Moreover,the flow patterns after bubble detachment is analyzed,and the boiling curves are compared with those pool boiling ones.更多还原