Water hammer induced by fast acting valves - experimental studies at Pilot Plant Pipework

Water hammer and inertia-driven cavitation hammer phenomena caused by the activation of fast acting valves were studied in a pipeline test facility at Fraunhofer UMSICHT in the context of the EURATOM project WAHALoads. The main goal of the project is the prediction of the loads on equipment and support structures. The presented experiments tackle some scenarios typical for power plants and supply material for the code validation with regard to the modelling of both thermal hydraulic effects and fluid-structure interaction. The test facility Pilot Plant Pipework (PPP) representing an approximately 230 m long experimental pipeline was upgraded in order to allow experiments at system pressures of up to 30 bar at maximum temperatures of about 180 °C. The test rig was furthermore equipped with a test segment that simulates a piping system and the associated supports typical for a (nuclear) power plant. For a better understanding of thermal hydraulic processes during cavitation behind the fast acting valve, novel instrumentation was applied. Wire mesh sensors as well as local void probes were equipped with integrated micro-thermocouples and used for the local instantaneous measurement of both void fractions and fluid temperature. The fast temperature measurement combined with the instantaneous detection of the passage of the gas-liquid interface measurement reveals insights into the condensation heat transfer controlling the speed of the void collapse in case of a condensational water hammer.