Hydraulic admittance of a partially saturated microfluidic slit

Abstract

Hydraulic admittance measurements have previously been performed on simple capillary systems as well as complex porous media such as gas diffusion layers. However, the theory for hydraulic admittance has yet to be developed for noncylindrical geometries in 2D channel studies. Here, hydraulic admittance theory is developed for a slit and experimentally measured for several hydraulic lengths (or partial saturation levels). Finite element modeling was included to address entrance effects associated with the sample. Both the theory and finite element modeling predicted higher hydraulic admittance magnitudes than measured, but the modeling predicted the resonance peak position better than the theory. The weak agreements to both the theory and modeling were mainly attributed to the slit approximation for the sample and additional interfacial curvature. Nonetheless, the resonance peaks were found to shift toward lower frequencies and decrease in magnitude with increasing hydraulic length for the theory, finite element modeling, and measurements.