Cavitation inception by almost spherical solid particles in water

The tensile strength of water increases when solid particles are filtered out, and it becomes greater the smaller the remaining particles are. Natural particles are of random shape, making parametric studies on the relationship between tensile strength and particle characteristics difficult. In this investigation, using degased tap water from which natural particles larger than about 1 (m were filtered out, the tensile strength was measured before and after seeding with almost spherical solid balls of diameters from 3 (m up to 76 (m. The smallest balls, though hydrophobic and notably larger than the remaining natural nuclei, had no measurable influence on the tensile strength. Seeding with balls at least a factor of ten to forty larger than the largest remaining natural nuclei reduced the tensile strength by only between 1/3 and 2/3 of that measured for the unseeded filtered water. On this basis it is concluded that a greater tensile strength is connected to the almost spherical solid balls than that connected to natural particles of the same size. The critical cavities developed from the larger balls had radii much smaller than those of the balls themselves. This supports the hypothesis that the cavitation nuclei are related to the fine scale surface structures observed on the balls. A model of their development is presented.