The Analysis Of Transient Flow And The Experiments Of Valveless Micropump With Diffuser/Nozzle Elements

Piezoelectric micropump is the core component of the Micro-fluidics-system which was applied to chemical analysis, drug delivery, chip cooling and so on.Micropump was developed rapidly in the last two or three decades. In this paper, the diffuser/nozzle piezoelectric micropumps and diffuser/nozzle elements were studied by experiments and simulations. The factors which have effect on the efficiency of micropump were classified into two categories: excitation parameters and structure parameters. The influence of volume change rate of the pump chamber, excitation frequency and diverging angle on efficiency were investigated. The the amplitude of the membrane ranges from 0.5 μm to 80 μm, the excitation frequency ranges from10 Hz to 5000 Hz, diverging angle ranges from 5 ° to 60 °.The deformation of the membrane was measured by laser doppler vibrometer and compared with the model proposed by Bu et al.. The results show that the model was accurate. The model provided a correct boundary condition for simulations. The performance of the micropump is predicted by numerical simulation.The simulation results agree with the experiment results very well. It proved that the simulations were correct and provided a basis for transition enhancement. Statistical analysis of the location and duration of vortexes in internal flow field is used to reveal the relationships among efficiency, diverging angle, frequency and chamber volume change rate. As the frequency ranges from 100 Hz to 1000 Hz, the efficiency increases sharply because the tube is blocked by vortexes at suction stage. The vortexes in the diffuser/nozzle elements is brought by the great adverse pressure gradient at the high frequency.The steady flow test bench was used to investigate the micro-channel which diverging angles were 20°, 40° and 60° under low Reynolds numbers. The distribution of velocity in micro-channel was observed successfully by CCD camera.There was no boundary separation when 20° micro-channel reached the maximum tube efficiency. However, There were two vortexes on both sides of the mainstream when 40° and 60° micro-channel reached the maximum tube efficiency. Themicro-channels with diverging angles ranging from 5 ° to 60 ° were studied by simulations when Reynolds number ranges from 100 to 1500 and frequency ranges from 0 to 5000 Hz. In steady flow, the optimal diverging angle was defined. According to the distribution of velocity in micro-channel, we believed that the optimal diverging angle is the maximum angle when the phenomenon of boundary separation or thickening of boundary layer doesn’t exist. In unsteady flow, the tube efficiency is almost constant when frequency is less than 100 Hz. Hence, the unsteady flow study could be replaced by steady flow study when the analysis is qualitative( f(27)Hz100). As the frequency is larger than 100 Hz and Re=100, the tube efficiency decreases with an increase in frequency; as Re=1500, the tube efficiency increases with an increase in frequency. When Reynolds number is 700, the tendency of tube efficiency and flow characteristic in tube correspond with the pumps’. Consequently,the investigation of micropumps could be replaced by the investigation of micro-channels which can simplify the objects.