A Novel Valveless Piezoelectric Micropump Based On Coanda Effect

Microfluidics systems applied to micro fluid controlling, micromixing and ingredient analysis show the great potential in the fields of chemical analysis, biotechnology, microchip cooling and micro fluid supply, etc, for their advantages of mini size, low power consumption, fast response and high accuracy. A series of micropumps, which are the transport devices in the microfluidics system, are developed according to different requirements. The valveless piezoelectric micropump is a hot topic of the micropumps for its simple structure, high integration, low power consumption, fast response and anti-electromagnetic interference. However, the typical valveless piezoelectric micropump with diffuser/nozzle elements is lower both in the flowrate and volume efficiency.The first valveless piezoelectric micropump applying Coanda effect is developed in this paper. The flowrate and the volume efficiency of the novel micropump can be significantly improved compared with those of the micropump with diffuser/nozzle elements. Additionally, the bidirectional flow of the micropump can be achieved by controlling the direction of the wall-attached jet. The main work and conclusions are listed below:1. The displacement model of double-layer vibrator proposed by Bu etc corresponds better with both the results of the numerical simulation and the experiment than the other three common simple models. As the radius of the piezoelectric ceramics to that of the elastic plate ratio is 0.1, the predictions of these three simple models all behave a large deviation with the results of the numerical simulation. When the ratio comes to 0.5, both the models’ predictions of the thin circular plate with uniform and central concentrated load fit the simulation result well. When the ratio is 0.9, the parabolic model’s prediction is proved more accurate compared with the simulation results. The experiment aiming to measure the displacement of the piezoelectric actuator is carried out with the microscope-based laser displacement meter. The results show that the prediction of the displacement model by Bu etc coincides well with the experimental data.2. A valveless piezoelectric micropump with single chamber based on the Coanda effect using the unsymmetrical three-way tubes is developed with the better performance than the same other micropumps with diffuser/nozzle elements at lower Reynolds numbers. The numerical simulation is done to study the impacts of the Reynolds number and the frequency on the flowrate. The results suggest that the flowrate increases with the Reynolds number and decreases with the frequency. The volume efficiency has a variation of direct proportion with the Reynolds number approximately. The vortexes generated by the rapid variation of the velocity in the Coanda jet element impact obviously on the performance of the micropump. Then a prototype was fabricated with PMMA by the precision machining and the thermal bonding, and tested for its flowrate and output pressure at different voltages and frequencies. It reveals that the fluctuation of the flowrate is larger at lower frequencies but less at high frequencies. The flowrate nearly decreases linearly as the back pressure rises, and the slope decreases with the frequency increasing.3. Based on the work above, an improved valveless piezoelectric micropump with single chamber is proposed by modifying the connection of the chamber with the three-way tube into a fillet. The numerical simulation demonstrates a volume efficiency over 0.5 at high Reynolds numbers. The response surface methodology is carried out to optimize the length and the arc surface width of the three-way tube. As the output pressure is 5 kPa, the predicted volume efficiency by the response surface is 0.323 with a error of only 1.9%with the simulation value 0.317.4. A bidirectional valveless piezoelectric micropump based on Coanda effect with double chambers is developed to achieve the bidirectional flow by controlling displacements of the two vibrators. The impact of the three-way tube angle and the ratio of the flowrates from the two chambers on the performance of the micropump is studied in the numerical simulation. It suggests that as the angle is smaller and the ratio is larger, the pressure difference is little between two sides of the jet, leading to a drop of the flowrate. The micropump is fabricated by PMMA and tested in the experiment for the performance. As the two vibrators work synchronously, the flowrate and the output pressure increase with the ratio of the voltages driving two vibrators. When the ratio is 0.6, the flowrate and output pressure reach 0.408 ml/min and 3.18 kPa, respectively. Those are 57% and 78% larger than those with single chamber respectively.5. A bidirectional valveless piezoelectric micropump based on Coanda effect with three chambers is presented. It is larger in the volume changes of the chambers, the angles between the tubes connected with the opposite chambers, leading to more pressure difference between two sides of the wall-attached jet and more entrainment fluid as well as larger volume efficiency.6. A serial valveless micropump with double chambers based on Coanda effect is developed by connecting two micropumps with single chamber in series. Larger flowrate and output pressure as well as the basically continuous flow of the micropump can be achieved compared with every single component. Besides, optimizing the orifice can improve the impact force, resulting in a batter performance of the micropump.7. The micropump with three chambers mentioned above can be improved by adding a synthetic jet element to obtain larger flowrate and continuous flow for both the inlet and the outlet with high frequency. The results of the numerical simulation suggest that the synthetic jet contributes much larger flowrate than the Coanda effect. However, the output pressure is lower due to the little flow resistance along the channel between the inlet and the outlet.