A numerical analysis of the unsteady flows in conical microdiffusers appropriate for valveless micropump applications is performed. The rectification efficiency of the diffuser valve is calculated directly as a function of geometric and operational parameters, including diffuser angle, diffuser slenderness, sizes of actuation chamber and inlet/outlet port, actuation frequency, and amplitude of actuation pressure. The computational results show that the diffuser with diverging angle of 10° and slenderness of 7.5 has the best rectification performance. For large actuation pressure amplitude, the optimal rectification efficiency and its corresponding Roshko number are relatively high. At the optimal Roshko number, the flow impedance is found to be dominated by fluid inertia. Sizes of the pump chamber and inlet/outlet port are shown to have a prominent effect on valve performance. Small actuation chamber or small inlet/outlet port can significantly deteriorate the valving performance of the diffuser.
