Fluid-solid Coupling Model For Valveless Piezoelectric Micropump Applying Coanda Effect

A fluid-solid coupling dynamic model is built to forecast the performance of valveless piezoelectric micropump applying Coanda effect.A vibration model involved with load of fluid pressure is presented for piezoelectric diaphram with two-layer structure. The model is based on the theory of sheet with small deflection and is in consideration of the two-layer structure that piezoelectric ceramic and elastic supporting plate. The high-order non-homogeneous vibration equation is solved by being divided into a homogeneous Bessel equation and a non-homogeneous static equation according to the superposition principle. The amplitude of the piezoelectric diaphram driven by voltage against the load of fluid pressure can be obtained from the solution of the vibration equation. The vibration model predicts the first order natural frequency of the diaphram without radial or circumferential nodel line on it. The amplitude of the piezoelectric diaphram with no load calculated by this model is tested by experimental data measured with laser.The Si-based valveless piezoelectric micropump applying Coanda effect is fabricated by sealing technology of anodic bonding. The principle of the micropump is analyzed by theory and numerical simulation. The detail working progress of the micropump are investigated though the flow field calculated by numerical simulation.The method of the numerical simulation is tested by the high-speed photograph experiment. The influences of several parameters including the diffuser angle, the Reynolds number and frequency are studied by numerical simulation respectively.The results indicate that the valveless piezoelectric micropump applying Coanda effect conveys fluid by the asymmetric outflow caused by the Coanda effect. There are three conditions including the suction, the attaching- wall and attached-wall condition within a working cycle in sequence. Whether the chamber jet attaches the wall can impact on the output performance of the micropump remarkably.Appropriate diffuser angle(from 30°to 45°) and high the Reynolds number as well as low frequency benefit the attaching to wall of the chamber jet. In the attached-wall condition, the volume efficiency of the micropump can achieve over 50%.The instantaneous flow model of the fluid within the Coanda element is presented. The energy of the fluid within the micropump is expressed by unsteady Bernoulli equation. The head loss with unsteady item and its coefficients are defined.Based on the results of the numerical simulation, hypotheses are presented about linear instantaneous flowrate of inlet in the attaching-wall condition and of entrained fluid of outlet in the attached-wall condition. The relative coefficients are measured by the numerical simulation. The instantaneous flow model is built on the unsteady Bernoulli equation and quation of continuity. The numerical simulation results suggest that the instantaneous flow model can predict the pressure in chamber of the micropump accuratly.A fluid-solid coupling dynamic model is built to forecast the performance of valveless piezoelectric micropump applying Coanda effect and is tested by the experiment. The equation set of the model is solved by iterative solution method. The convergence procedure is discussed and relative dimensionless residual errors as well as the thresholds are defined. The performance of the micropump are predicted by the model, including the instantaneous pressure and flowrate of chamber and the flowrate of the outlet. The the first order natural frequency of the diaphram is calculated in the wet mode without radial or circumferential nodel line. The results show the frequency where the micropump has the largest flowrate is after the natural frequency of the diaphram in wet mode. The maximum output flowrate and amplitude are measured in the output characteristic experiment system or by the laser. The experimental data are compared with the outcomes from the model. The results suggest that the fluid-solid coupling dynamic model can predict the performance of the valveless piezoelectric micropump applying Coanda effect well as it works near the natural frequency of the diaphram in wet mode.