Study on Micropump Using Boiling Propagation Phenomena

研制了一种利用沸腾传播现象的微泵。在以脉冲方式加热的薄膜加热器上，通过在局部高热麻段上产生蒸汽泡来触发沸腾，并在加热器的长度上实现了单向沸腾传播。研究了沸腾传播的加热功率条件、传播形态、气泡大小和传播速度。在u型微通道中，通过沸腾传播以高达20 Hz的频率重复进行连续泵送作用，已被通道垂直截面中液体柱之间产生的水头差所证实。净流速也被测量在高达40赫兹的频率从半月板的位移管在相同的高度水平出售。通过使用较小的加热器和/或选择衬底材料和成分，可以在重复脉冲加热期间抑制衬底的温度升高，从而实现更高频率的泵送。从这一观点出发，基于从加热器到邻近材料的热传导的数值模拟，预测了在使用快速沸腾的微致动器脉冲加热过程中，加热器时间平均温度升高能保持在允许范围以下的最大频率。结果表明：在一定的脉宽和温度条件下，随着加热器尺寸的减小，允许频率显著增大；加热器尺寸、脉冲宽度和衬底性质对频率的影响在很大范围内与控制该现象的无因次量相关。模拟的重复频率与沸腾和不沸腾的实验结果一致。

A micropump which uses boiling propagation phenomena has been developed. Boiling has been triggered on a film heater, which is heated in a pulsewise manner, by generating a vapor bubble on a local high heat flax section, and unidirectional boiling propagation has been realized over the length of the heater. The heating power conditions under which boiling propagation occurs, configuration of propagation, size of bubbles and propagation velocity have been examined. Continuous pumping action in a U-shaped microchannel via boiling propagation repeated at a frequency of up to 20 Hz has been confirmed by the head difference generated between liquid columns in the vertical section of the channel. Net flow rate has been also measured at a frequency of up to 40 Hz from the displacements of the menisci in tubes both vended horizontally at the same height.Pumping at higher frequencies will be enabled by applying a smaller heater and/or choosing the substrate material and composition such that the temperature increase of the substrate would be suppressed during the repetition of pulse heating. From this viewpoint, the maximum frequency at which the increase in time-averaged heater temperature can be maintained below an allowable limit during pulse heating in microactuators using rapid boiling has been predicted based on a numerical simulation of heat conduction from a heater to adjacent materials. The results show that the allowable frequency increases significantly with a decrease in heater size for prescribed conditions of pulse width and temperature increase. The effects of heater size, pulse width and properties of substrate on the frequency have been correlated over wide ranges in terms of the dimensionless quantities governing the phenomenon. The simulated repetition frequency agrees with the results obtained from experiments both with and without boiling.