Elimination of cavitation induced vibrations in orifice plates

Abstract

Increasing cavitation in a flowing liquid in a pipe system is associated with increasing levels of sound or noise and vibrations. It can lead to large loads if steam bubbles implode close to the pipe wall, which can be harmful to the pipe system. It can lead to fatigue due to vibrations and even worse, erosion of the pipe wall. In the worst case, it can lead to a pipe break. Therefore, cavitation is essential to be predicted and prevented in system design. The aim here is to experimentally verify a concept for the elimination of strong cavitation and harmful cavitation induced vibrations. It has been experimentally demonstrated that replacing a conventional orifice plate with three stages of multi-hole orifice plates in series with only a total streamwise distance of two pipe diameters, giving the same total pressure drop, is sufficient for the elimination of strong cavitation. The cavitation induced vibration levels are reduced by almost 500%. The streamwise distance is almost 500% shorter if multiple conventional orifice plates were to be employed. The same conclusions hold for tests performed with β = 0.30 and 0.40. This compact design was successfully applied at a nuclear power plant, and the reduction of the cavitation induced vibration levels was confirmed. The main contribution is the quantification of the vibration levels, how they depend on the type of orifice plates (conventional, multi-hole, and multi-stage-multi-hole), and how they scale with the dynamic pressure. This will be used for the validation of future CFD simulations including Fluid Structure Interaction (FSI) and advanced two-phase models.