The onset of cavitation in pressure dropping devices in water and sodium

Cavitation tests are described on multi-hole nozzle plates and wire meshes approximately 100 mm diameter in water at 200C and sodium at 3000C. The performance of a plug seated in a cylindrical bush with a small annular clearance is also given. These pressure dropping elements were mounted in recirculating loops where cavitation was induced by lowering the background pressure at constant flow. Cavitation was detected acoustically using wall mounted piezoelectric microphones, the signal being displayed on a ratemeter recording individual cavitation events. For nozzle plates cavitation started intermittently as the pressure was lowered, the noise level suddenly increasing at a critical cavitation number sigmasub(i). For meshes and the plug-bush unit the intermittent region was absent. For all cases values of sigmasub(i) in water and sodium were similar, the poorest agreement being for the plug-bush unit. (author)