A micropump is a crucial component in a microfluidic device, as it could generate accurate tiny amounts of fluid and hence reduces the reagents cost and shortens the analysis time. A conventional pump requires valves, which are difficult to be assembled when reduced to micro scale. Hence valveless pump would be the obvious solution.

To achieve the flow directing capability, gradually expanding/contracting diffuser/nozzle elements are used as the “fixed valves” in valveless micropumps. The fluid flowing along the nozzle direction receives a larger pressure loss than that along the diffuser direction. Therefore, with periodic oscillation of the flow, there would be a net flux along the diffuser direction. Based on previous researches, the performance of a valveless micropump primarily relies on the flow-directing capability of the diffuser/nozzle element, which is also known as diffuser efficiency, η. A higher η means a higher flow-directing ability and thus, a larger flux of a valveless micropump.

There are many researchers attempting to maximise η. In this work, a new diffuser/nozzle structure with extended sidewalls at the large end, named as “lips”, is proposed, investigated and simulated. Introducing more frictional pressure loss in the nozzle direction, the “lips” could increase the η by a maximum of 31%, which correlates to an improvement of 23% for the net flux of the entire micropump. Later, more simulations with different lip lengths, thicknesses and extended angles of the “lips” were also investigated and compared. The results show that η increases with the “lips” length at the beginning and reaches a peak at some length. Further, the thickness of the “lips” has nearly no influence on the performance improvement. Finally it was found that the highest η occurs when the “lips” are almost perpendicular to the outlet plane.

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