| Micropump is one of the most important fluid-driving elements for biochips. Its structure and pumping behavior play an important role to efficiency of biochip systems. It is needed to investigate periodical flow behavior for a high-performance micropump. Currently there are many types of micropumps. Flat-walled valveless diffuser micropump has advantages of easy fabrication, long life, low costs and high reliability. The periodical flow characteristic of micropump is numerically studied in this work.This paper employs shallow water model to approximate the three-dimensional flows of a thin pump chamber to a two-dimensional thickness-averaged flows. The finite element method and pressure correction algorithm are used to solve the horizontal flows of the pump, calculate the flow rate and investigate backpressure characteristics. The numerical results indicate that (1) Time phase differences of periodical flows and backflows occur in diffuser. (2) A pair of symmetric vortexes appears near outlet of pump chamber by the end of suction phase. (3) Phase difference occurs between periodical flow and periodical pressure. (4) The directional flow rate of the pump is governed by nonlinearity of Navier-Stokes equations. Furthermore, the quantitative relations of the pump flow rate and the geometry size of diffuser, the driving frequency of piezoelectric diaphragm and fluid viscosity are also given in numerical examples of this paper. A high-performance pump can be possibly achieved by optimizing pump parameters.In addition, the numerical simulation of three-dimensional flows of the micropump is also carried out using the computational fluid dynamics software package FLUENT in this paper. The simulation results show that the same flow phenomena have been found as those predicted by two-dimensional shallow water model. The directional flow rate of micropump predicted by FLUENT is in the same order of magnitude as the shallow water model.
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