Preliminary experience with a new compact disk apparatus for cavitation erosion studies

Abstract

When bubbles collapse near solid surfaces, cavitation damage can occur. Two are the already known erosion mechanisms: liquid micro-jets impingement and shock waves. These micro-jets and shock waves are responsible for material loss from the surface, basically by wear failure. In the rotating disk device, a disk with cavitation inducers and specimens fixed on it rotates inside a water chamber to provide cavitating flow. In this work, a new concept of the horizontal rotating disk device is presented and discussed, as well as some preliminary results obtained from its operation. This new compact apparatus is tested with the aim to observe its performance in generating bubbles and to cause erosion. The damage in the specimens is measured by mass loss and surface observations by photographs of the tested specimen surface obtained by scanning electronic microscope, which are shown and discussed. After 15 h working in cavitating conditions, pure aluminum and brass were eroded by the cavitation phenomenon, resulting in pitting formation and mass loss. Also, 1020 mild steel specimen was investigated for 5 h. The new presented version of the equipment is cheaper and more compact than the preceding ones, resulting in advantages related to initial costs and losses in power transmission. The specimens of aluminum, brass and steel, were eroded by cavitation although in the aluminum the mass loss was lower than expected. The brass specimen was eroded as expected. The erosion mechanism is possibly due to bubbles collapse and water jet impact perpendicular to the specimen surface, producing circular erosion craters. Burned circular craters were also seen in the aluminum specimen.