Liquid Column Separation Due to Fluid Hammer Occurrence in Propellant Lines

Abstract

When a pressurized liquid enters a pipeline with a closed end and under vacuum conditions, the resulting liquid front suddenly is brought to rest at the end of the pipe. This type of flow configuration is found in propulsion systems of satellites during priming operation and induces a fluid hammer followed by a column separation, generating a multiphase gas/vapor bubble. This paper aims at explaining the column separation mechanism by solving the momentum equation for the liquid column moving in the pipeline when column separation occurs and by applying the integral form of the conservation principles to expansion and compression waves within the flow. The resulting model provides the velocity and position of the liquid front during column separation. Thus, the size and duration of the multiphase bubble can be determined, and the variables involved in the process are identified, which helps the analysis of applications where this complex phenomenon is involved. It is shown that the initial velocity of the liquid front during column separation is the main parameter, which itself is a function of the fuel tank pressure and the fluid hammer pressure rise. The comparison of the predictions with experimental data shows an excellent agreement.