Water hammer induced by fast-acting valves: Experimental studies at pilot plant pipework

"The 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 code validation with regard to the modeling of both thermohydraulic effects and fluid-structure interaction. The test facility Pilot Plant Pipework, 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 further 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 thermohydraulic 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 microthermocouples 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 the case of a condensational water hammer. Two-phase flows commonly occur in nature and in a multitude of other settings. They are not only of academic interest but are found in a wide range of engineering applications, continuing to pose a challenge to many research scientists and industrial practitioners alike. Although many important advances have been made in the past, the efforts to understand fundamental behavior and mechanisms of two-phase flow are necessarily a continuing process. Volume 8 of Multiphase Science and Technology contains the text of the invited lectures given at the Third International Workshop on Two-Phase Flow Fundamentals sponsored by the Electric Power Research Institute (EPRI) and the U. S. Department of Energy (DOE). Many of the world's foremost researchers, representing diverse cross sections of multiphase flow community, attended the workshop. The diversity of the participants enriched the discussions and conclusions that were reached. The purpose of the workshop was to define the state-of-the-art in two-phase flow, advance the science, and reach a consensus on future research directions. In particular, the specific emphasis was to evaluate the current understanding of the physics of multiphase flows as based on measurement and visualization, to evaluate the current state of the art in modeling of multiphase physics, to develop an agreed-upon basis for the balance equations for multiphase systems and their associated boundary conditions and closure relations, to evaluate and discuss the mathematical structure of the equations to describe multiphase flow, and to discuss and identify the methodologies needed to apply proper numerical procedures for the solution of the governing equations; that is, to fill existing gaps and bring together materials from diverse fields of multiphase flow. Multiphase Science and Technology is now being published as a quarterly journal, a mode of publication that will allow the material to be published more rapidly and regularly. Please contact Begell House for information on the previous eight hardbound volumes.