Analysis of transient flow characteristics in flat diffuser/nozzles

Transient flow characteristics in piezoelectric micropumps with flat diffuser/nozzle tubes were studied by numerical simulation. There is phase difference between velocity and pressure at high frequency. The effect of Reynold number, diffuser angle and excitation frequency on phase difference was studied. Pressure loss coefficient and tube efficiency were discussed as Womersley number ranging from 0.24 to 1.50.The existence time of visible vortexes in chambers decreases with the increasing of frequency. The tube efficiency of Re = 200 and f = 10 Hz reaches maximum when θ is 12°. The phenomenon of wall attached jet in the diffuser/nozzles at high Reynold numbers and low frequencies is paid attention to. When the frequency is greater, the Coanda effect disappears.