Study on Micropump Using Boiling Propagation Phenomena

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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.