The Flow Behavior Study Of The Liquid-Solid Coupled Micropump System For Boichips

Micropump (or microactuator), one of the most important fluid-driving elements in Micro-Electronic-Mechanical System, has extensive applications in many fields. Micropump is not miniaturization of macropump, but a complex micro-system involving many coupling physical factors including liquid, solid and piezoelectricity. Dynamic coupling study of multi-physical factors of micropump has not been well established. Micropump analysis and optimal design is a difficult task. The objective of this work is to develop an effective mathematical model and numerical algorithm to guide optimal design of micropumps.According to the working behavior and the structure characteristics of the piezoelectric micropump, the shallow water model is used to simulate the periodical flow in the micropump in this work. The profile of the flow velocity in the thickness of the micropump is approximated by the periodical Poiseuille flow between two infinite plates. Employing integral-average method in thickness to approximate the periodical flow in micropump, a nonlinear shallow water equation and Poisson equation of fluid pressure were presented to characterize the flow in the micropump. Using Galerkin finite element method and ignoring the nonlinearity a matrix equation of fluid pressure is obtained. Coupling the fluid pressure equation with the vibrating equation of the diaphragm, a fluid-structure interacting equation was obtained to characterize the working behavior of the micropump.A mode analysis of the liquid-solid coupled micropump system is carried out to calculate the natural frequencies of the micropump and the vibration shape of the silicon diaphragm. The results of the model analysis of the micropump system indicate that the natural frequencies of the micropump system are much lower than those of the uncoupled system; especially the first order natural frequency significantly decreases due to the interaction of liquid and diaphragm. The flow rate of the micropump reach to the peak value when the frequency of the external voltage is close to the natural frequency of the micropump system. The external frequency for maximum flow rate is slightly higher than the natural frequency of the micropump.Flow analysis of the micropump is conducted to investigate fluid pressure, pump flow rate and periodical flow behavior. The numerical results indicate that the periodical flow in the pump chamber is much similar to the flows induced by a point source, the exhaust flow in the first half period, and a point sink, the suck flow in the second half period. It is also found that a back flow and vortices appear in the chamber. The fluid pressure is almost uniform in the chamber center and rapidly varies in the region close to the micro-diffuser.This work also studies the quantitative effects of the structure parameters of the micropump (the pump thickness, the radius of the piezoelectric patch, the length, the minimum width and the opening angle of the micro-diffusers) on pump working performance (the natural frequencies of the micropump, the diaphragm amplitude and the pump flow rate). The numerical results indicate that the natural frequency of the micropump decreases with the decrease of the pump thickness, and increases with the increase of the ratio of radius of the piezoelectric patch to the pump chamber radius. When the open angle of the diffuser is in the range of (5o ~ 20o ) the natural frequency of the micropump increases with the increase of the open angle and the minimum width of the diffuser. The flow-rate achieves a maximum value when the open angle is about 15o. There exists an optional minimum width of the diffuser, so that the pump flow-rate and the diaphragm amplitude reach peak values.The mathematical model and numerical results presented in this study are useful to optimal design of the micropump in biochips and microfluidic analysis system.