Fluid–structure coupling in valveless micropumps

Abstract

Valveless micropumps work on the principle that the reciprocal forcing of fluid by an actuator through diffuser/nozzle elements generates a rectified mean flow. The pump characteristics depend on the coupling between the fluid and structure. We analyze the characteristics of valveless micropumps by developing a coupled model for the area-averaged membrane displacement and the rectified flow through the diffuser/nozzle elements. Analytical expressions are derived for the pump flow rate Q and pressure drop ΔP characteristics as functions of the forcing frequency. The predicted natural angular frequency is compared against published results and the agreement is reasonable. The model shows that the maximum flow rate Qmax satisfies Qmax ∼ ω for ω/ωN < 1, and Qmax ∼ 1/ω for ω/ωN > 1, which is supported by published experimental data. The maximum pressure ΔPmax satisfies ΔPmax ∼ ω2 for ω/ωN < 1, ΔPmax ∼ 1/ω2 for ω/ωN > 1. The available experimental data are sparse (in comparison to Qmax). The general model is applicable to all valveless micropumps which incorporate diffuser/nozzle elements.