Influence of Liquid Length Variation in Hydraulic Transients

Abstract

When a problem of hydraulic transients with entrapped air in pipelines and/or with water‐column separation is tackled, the variation of the length of the liquid column is not usually taken into account. In this paper (due largely to the assumption of a system with a cross section at the air‐water interface in a horizontal pipeline), it is shown that in a system with entrapped air and without changes of potential energy at the air‐water interface (horizontal pipe) the final pressure obtained in a mass oscillation in which the kinetic energy of the fluid and the liquid column length variation are neglected is the same as the final pressure obtained from the consideration of both effects. This peak pressure is also independent of the assumed polytropic exponent for the entrapped‐air compression. Nevertheless, the instant when the maximum is achieved is different.