Numerical characterization of the flow rectification of dynamic microdiffusers

In this study, a numerical investigation is presented to characterize the transient behaviors of microdiffuser pumps. The motivation of the present work is to clarify the scaling and dynamic effects on the flow rectification of microdiffuser pumps. Two primary parameters, half angle (θ = 5° to 55°) and excitation frequency (f = 1 Hz to 1000 Hz), are considered. A time-dependent sinusoidal pressure with fixed pressure amplitude is applied at the inlet as the boundary condition. Different from previous investigations and despite the corresponding low Reynolds numbers, circulation is observed for all tested half angles and excitation frequencies. The persistence of the backflow helps to augment flow rectification since the vortical structures block a portion of the diffuser and prevent the through flow from decelerating. Contrary to past claims, diffusers with larger half angles show better rectification effects for 5° ≤ θ ≤ 35°. For θ > 35°, the net flow rate is nearly independent of the half angle. The computational results also yield that the net flow rate is independent of excitation frequency for f 25 Hz. Hence, the role of excitation frequency is classified into three different regimes by the Roshko number: frequency independent regime (Ro 2). An essential contribution of this study is that it provides design guidelines for microdiffuser pumps, further expanding the knowledge of flow rectification properties to make more efficient use of microdiffuser pumps in various microscopic applications.