Fundamental Study on Micro-Actuator Utilizing Rapid Boiling

这项研究的目的是通过快速加热来揭示微小薄膜加热器或浸在纯液体中的细丝上产生的沸腾气泡行为，因为这种行为对于理解和设计利用加热器快速沸腾产生的气液相变的微执行器是必要的。对一台宽0.1 mm、长0.25 mm的薄膜加热器进行了直流脉冲加热，加热速率最高可达109K/S，测量了沸腾开始时的温度、成核气泡数量的变化、微气泡的长大过程、气泡的生长过程、破裂过程以及传热行为。对自发成核后的那些也进行了检查。在此基础上，提出了过热液层蒸发模型，从理论上解释了加热器气泡快速成核之前的换热和气泡行为。实验结果和理论表明，随着升温速率的增加，最大气泡体积减小。在很宽的升温速率范围内，用直径为0.05 mm的细丝进行了一系列的观测实验，结果表明，根据升温速率的不同，气泡的产生和破裂行为大致分为3种类型。讨论了每种类型对微执行器的适用性。在实际微致动器中用液体混合物代替纯液体，对二元液体混合物中的气泡成核进行了实验研究。

The objective of this study is to reveal the boiling bubble behavior generated on a very small film heater or a fine wire immersed in pure liquids by heating them rapidly, since the behaviors are necessary for understanding and designing the micro-actuator which utilizes the liquid-gas phase change resulted from rapid boiling on the heater. A film heater whose dimensions were 0.1mm in width and 0.25mm in length was heated pulsewise by a direct current with a heating rate up to about 10^9K/s at the maximum and the temperature at the inception of boiling, the variation of nucleated bubble numbers, the aggragation process of tiny bubbles, the growth process and the collapse process of a bubble were measured and analyzed as well as the heat transfer behavior. Those succeeding the spontaneous nucleation were also examined. Thus, the bubble dynamics and the heat transfer characteristics when a very small film heater was heated rapidly were wholy revealed.Further, with the aid of the above experimental results, the superheated liquid layr evaporation model was presented to explain theoretically the heat transfer and bubble behavior preceded by the rapid bubble nucleation on a heater. Experimental results as well as theoreticals showed that the maximum bubble volume decrased with the increase of the heating rate.A series of observation experiments were carried out with a fine wire of 0.05mm in diameter for a very wide range of heating rate and it was shown that the bubble generation and collapse behaviors were divided roughly into 3 types in accordance with heating rate. Applicability of each type for a micro-actuator was discussed. Bubble nucleation in binary liquid mixtures was studied experimentally, since liquid mixtures was used instead of pure liquid in real micro-actuator.