Condensation induced water hammer in thermal plants

Abstract

A contact of vapour and subcooled liquid in pipelines or vessels leads to the rapid condensation, the acceleration of the liquid column and its splashing on a closed end or onto other liquid volume, which results in very high pressure peaks that could destroy walls’ integrity. This phenomenon is known as the condensation induced water hammer (CIWH). Although it is known for decades, CIWH still occurs in various systems of thermal and nuclear power plants, district heating and cryogenic systems. Hence, there is a need to systematize thermal-hydraulic conditions that could lead to this accident, to permanently emphasize the safety aspects of this problem in engineering education, investigate specific effects important for the CIWH dynamics, and to develop and verify numerical methods for its prediction. In the paper a numerical model for the CIWH simulation and analyses is presented and applied to the prediction of intensive pressure waves propagation in two-phase pipe systems. The modelling approach is based on the two-phase flow model, tracking of the water column - steam volume interface and modelling of the direct steam condensation on the subcooled liquid. Obtained numerical results are tested against available experimental data. Complex transient thermal-hydraulic conditions that lead to the condensation induced water hammer in the feedwater system of the thermal power plant are simulated and analyzed. The safety system that prevents the occurrence of the CIWH at the feedwater system is presented and verified.