A New Micropump With Planar Passive Valves and Its Flow Measurement
Date Issued
2008
Date
2008
Author(s)
Hsu, Chia-Jui
Abstract
In this study, a novel micropump has been successfully developed by simple MEMS fabrication technique. Based on the concept of micro-TAS or Lab-on-a-chip, more considerations are taken into account when designing a new micropump. The design guidelines for the present micropump include (1) easy fabrication and high integration capability, (2) low power consumption and high pumping performance, and (3) high quality of the output flow. According to the present design guideline and the summary of previous literatures, two types of planar micropumps, single-chamber and double-chamber, were proposed and tested in the experiments. The periodic volumetric change of the pumping chamber provided a dramatic pressure gradient to drive the flow in oscillatory form. The planar passive valves were then actuated by the oscillatory flows. Based on the concept of electronic bridge converter, two single-chamber micropumps in parallel arrangement can transform an oscillatory flow into a steady-like flow at the outlet. In chapter 1, numerous researches of micropump in the past 30 years are introduced. The pumping principles and the elements of the earlier micropumps are also classified. Based on the previous studies and the design guidelines described in previous paragraph, the new patterns of the present micropumps and their pumping principles are given in chapter 2. The fundamental analyses including (1) the coupling effects between the chamber diaphragm and the fluids, and (2) the oscillatory flow behaviors and their effects on the valve motions are discussed in chapter 3. The transient flow behaviors in the micropumps were measured by externally- triggered micro-particle-image-velocimetry (micro-PIV) system. The measurement results provided very useful information of the flow fields and the valve motions in the micropump. The detailed experimental methods and procedures are given chapter 4. The results in chapter 5 indicated that either a single-chamber micropump or a double-chamber one could be activated at an excitation voltage lower than 10 V. At the driving voltages from 10 to 30V, the results revealed that there were uniquely linear relationships existed between the flow rates and driving frequencies for both micropumps. The linear regime of single-chamber micropump was at 0.1-0.8 kHz. Moreover, the linear regimes of double-chamber micropump were at 0.1-0.4 kHz and 0.1-0.5 kHz for in-phase and anti-phase operations, respectively. The linearity and repeatability were used to further characterize those linear regimes. The reliable linear regimes of those micropumps were favorable for the integration of micro-systems. The measurement results of transient flow behaviors and the valve motions clearly exhibited that the variation of the oscillatory flow had a phase leading with respect to that of the moving part. This phase difference increased with an increasing frequency, but reduced with an increasing voltage. The larger phase difference would lead to more leakage so that the flow-rectifying capability and the pumping performance were thus reduced. Moreover, the switch-off time of the valve was found to be mainly depended on the excitation voltage, i.e. shorter switch-off time could be obtained by using higher excitation voltage. The flow measurements of the double-chamber micropump in in-phase and anti-phase modes clearly revealed different flow behaviors at the outlet. In the in-phase mode, the phase-dependent flow velocities presented similar results to those of single-chamber micropump. On the other hand, the flow measurements using micro-PIV clearly demonstrated the process of how oscillatory flows were converted into smoothly continuous flows in anti-phase mode operation. In addition, the flow became steady-like continuous when at higher frequencies and better output flow quality was thus obtained in this experiment. The conclusions are given in the last chapter and indicate the major contribution of the current study. Some further studies such as the optimization of the flow-rectifying capability and the pump performance are also proposed. Moreover, a high-quality flow at the outlet of a reciprocating micropump, i.e. a nearly steady flow, can also be effectively obtained by this microfluidic device.
Subjects
novel planar micropump
planar passive valve
micro-PIV
micro flow-converter
linear regime
externally-triggered technique
Type
thesis
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