| description abstract | This paper introduces a novel method for preventing nozzle wear in abrasive water jets. It consists of using a porous nozzle, surrounded by a reservoir containing high-viscosity lubricant, which is exposed to the same driving pressure as the flow in the nozzle. The pressure difference across the porous medium, generated due to the high-speed flow in the nozzle, continuously forces lubricant through it. The resulting thin oil film forming on the walls of the nozzle protects the walls from the impact and shear caused by the abrasive particles. The porous nozzles were manufactured using Electric Discharge Machining and examined with Scanning Electron Microscopy. Two test facilities were used for evaluating the porous lubricated nozzles. The first was a two-dimensional facility, supporting a 145 μm wide nozzle with windows on both sides, which enabled visualization of the oil film and measurements of the liquid and abrasive-particle velocities using Particle Image Velocimetry. The measured slip velocities were also compared to computed values from a simple numerical model involving one-way coupling. The second facility used a 200 μm axisymmetric nozzle to determine the extent of nozzle wear under different conditions. We found that the presence of an oil film substantially reduced the extent of nozzle wear, from 111 percent of the diameter, when the nozzle was not lubricated, to 4 percent, when the oil viscosity was 1800 mm2 /s and its flow rate was 2.4 percent of the water flow (over the same period). The wear increased as the lubricant flow rate and viscosity decreased. The presence of the oil film also improved the coherence of the jet. | |
