LAUSR

The research and development of piezoelectric valve-less micropumps have become an increasingly popular topic for decades. A highly efficient valve-less micropump is necessary to deliver liquids for microfluidic control systems. Study of the flow mechanism in the valve-less micropump may help to further improve the pumping efficiency. In this paper, a dynamic finite element model is used to investigate the mechanism of a valve-less micropump with a diffuser/nozzle. The simulation result shows that the flow performance of a valve-less micropump is not only dependent on the diffuser/nozzle but is also related to the entire structure. When fluid flows through the nozzle, the chamber connected to the nozzle end is considered as a diffuser with an angle of 180°. This diffuser is located in the jet flow region, where the high velocity fluid generates a vortex in the interfacial area of the nozzle and chamber. Such a vortex works as a 'virtual valve', which can block the reflux and result in unidirectional flow. Besides, the vortex degree is tightly related to fluid velocity, which is determined by the input voltage. When the input voltage is larger than the threshold voltage (20 V), the virtual valve is activated, and the flow rate of the micropump increases rapidly with the input voltage. The simulation analysis conclusions are verified by experiment results. The experimental results demonstrate that the maximum flow rate of 5.4 ml min−1 is finally obtained, which is comparable to a typical valve micropump.