Fundamental Study on Micro-Actuator Utilizing Rapid Boiling

本研究的目的是揭示沸腾气泡的行为产生在一个非常小的薄膜加热器或细金属丝浸泡在纯液体快速加热，因为行为是必要的理解和设计的微驱动器，利用液-气相变引起的快速沸腾加热器。用直流脉冲加热宽0.1mm、长0.25mm的薄膜加热器，加热速率最大可达10^9K/s，测量了沸腾起始温度、成核气泡数变化、微小气泡聚集过程测量并分析了气泡的生长过程和溃灭过程以及传热行为。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上气泡快速成核前的传热和气泡行为。实验结果和理论分析表明，随着升温速率的增大，气泡的最大体积减小。用直径为0.05mm的细丝在很宽的升温速率范围内进行了一系列的观察实验，发现气泡的产生和溃灭行为按升温速率的不同大致可分为3种类型。每种类型的微致动器的适用性进行了讨论。由于在真实的微致动器中采用了混合液体而不是纯液体，因此对混合液体中气泡的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.