Temperature effects on water hammer phenomena in pipelines

Abstract

Water hammer, or hydraulic shock, occurs in pressurized pipelines when fluid flow is abruptly altered, leading to pressure surges. Even though this phenomenon can cause significant damage to systems, it is often overlooked during design phases of district heating (DH) networks. This paper investigates the impact of temperature on water hammer phenomena. Various modeling approaches are discussed, emphasizing the importance of considering both hydraulic and thermal transients. To assess the impact, we modeled and simulated a reference problem involving rapid valve closure in a copper pipe system, considering both cavitating and non-cavitating flow scenarios. The steady-state results show that the pressure head at the downstream end of the pipe increases with temperature due to decreasing density and is independent of the pipe material properties. The transient results reveal that higher temperatures lead to cavitation and more intense pressure peaks, which could be missed without considering thermal-hydraulic phenomena. The analysis of a practical problem involving a 1000 MW DH system in Helsinki showed that using a single wave speed for both supply and return lines underestimates pressure peaks due to partial wave cancellation. In contrast, temperature-dependent wave speeds provide more accurate predictions of pressure wave behavior, highlighting the importance of understanding these effects. Sudden pressure drops can trigger protective measures and lead to cavitation, weakening pipeline integrity over time. The findings underscore the importance of considering temperature-dependent properties in the design, modeling and analysis of DH networks to prevent potential damage and ensure system reliability.