Anomalous phenomena in pressure drops of water flows through micro-orifices

Abstract

Pressure drops were measured for high-velocity water flows through micro-orifices of various diameters. The observed pressure drop values agreed well with the values predicted by the Navier–Stokes equation for 400 and 100 μm diameter orifices, but were lower than the predicted values for orifices less than 50 μm in diameter. In particular, the measured pressure drop value was almost two orders of magnitude lower than the predicted value for the 10 and 5 μm diameter orifices. Several factors that may cause a reduction in pressure drop were considered, including orifice shape and deformation of the orifice foil, but none proved to be significant enough to cause such a large reduction. Elastic stress in orifice flow appeared to be the most plausible cause of the pressure drop reduction. The elastic stress, which was estimated by the jet thrust method, was found to be dependent on the mean velocity passing through the micro-orifices, which strongly supported the elasticity of water flows.