Is There a Best Fixed-Geometry Valve for Micropumps?

Abstract

Two frequently used geometries for fixed-valve micropumps are the nozzle-diffuser and Tesla-type valve. However, little work has been done to investigate the relative merits of optimal shapes for each type of valve. In this study 2D steady-state computational fluid dynamics coupled with a formal optimization procedure and experimental evaluation were performed to address this problem. Non-dimensionalization of the problem allowed a comparison of the two valve types independent of physical size, i.e. shape alone was studied. Optimal shapes were found based on maximizing calculated diodicity as a function of Reynolds number in conjunction with a weighting function used to control forward pressure drop. The optimal shape for each valve was then compared numerically and experimentally to reference valves similar to those reported in the literature. The optimal shape for each valve type was found to be significantly different from the reference shape and exhibited significantly improved performance. Both valve types achieved a maximum diodicity of approximately two in the range of Reynolds number 0 ≤ Re ≤ 2000. The optimal Tesla-type valve was characterized by a large return loop and shallow return loop angle. The optimal nozzle-diffuser was characterized by a very long diffuser section that prevented flow separation in the forward flow direction along with increased wall shear stress in the reverse flow direction. The diodicity vs Reynolds number curve for the Tesla-type valve monotonically increased, while the nozzle-diffuser exhibited a local maximum in the mid-Reynolds number range. These characteristics may play an important role when valve size is determined to maximize resonant behavior of a micropump. Thus they influence numerous pump design criteria such as target flow rate-pressure characteristics and overall pump size.