Water-hammer control in pressurized-pipe flow using an in-line polymeric short-section

Abstract

Water-hammer control strategies constitute an essential and critical task for both hydraulic designers and manufacturers to ensure the global economic efficiency and safety operations of hydraulic utilities. The primary objective of this paper is to present an alternative strategy to control water-hammer up- and down-surges, induced into a steel piping system. The proposed technique is based on replacing a short-section of the transient sensitive regions of the existing piping system by another one made of polymeric material. Two types of polymeric materials, used for the short-section and including high- or low-density polyethylene (HDPE) or (LDPE), are addressed in this study. The 1-D pressurized-pipe flow model is used to describe the hydraulic system, along with the Ramos formulation, based on two decay coefficients being used for considering the pipe-wall viscoelastic behavior and unsteady friction effects. Numerical computations were performed using the fixed-grid method of characteristics. The efficiency of the numerical model is first verified against experimental data available from the literature. Thereafter, critical flow scenarios relating to water-hammer up- and down-surges, including a cavitating flow, are revealed and discussed to point out the efficiency of the used protection technique. From the case studied, it is found that such a technique could mitigate critical water-hammer surges and, hence, might greatly enhance the reliability of the industrial hydraulic systems and urban water utilities, while safeguarding operators. Despite the available protection measures, the utilized technique can substantially soften both up- and down-surge waves induced by severe water-hammer events. It is also found that the amortization of pressure rise and pressure drop is slightly more important for the case of a short-section made of LDPE polymeric material than that using an HDPE polymeric material. It is also observed that other factors contributing to the damping rate depended upon the short-section length and diameter. In fact, the examination of the pressure peak magnitude sensitivity, with the short-section length and diameter being the controlling variables, provides optimum values of these parameters for sizing the replaced polymeric short-section.