(40ak) CFD Simulation of Flow Behavior Under Condensation-Induced Water Hammer in Horizontal Pipe

CIWH (Condensate Induced Water Hammer) is a severely recurring problems in steam line system. It occurs when a steam pocket becomes totally entrapped in subcooled condensate. Steam meets the condensate and instantly gets condensed to liquid water with a volume reduction of more than 1000 times triggering the adjacent liquid to fill up the vacuum space and resulting in water hammering. The hammering source continuously propagates to other parts of the pipeline. The volume once occupied by steam shrinks, and the pressure in the void drops to the saturated vapor pressure of the surrounding condensate. The phenomenon is similar to that of rapid steam bubble collapse following high pressure shock. Therefore, starting up the HP steam line containing condensate can be catastrophic at times and the attempt to drain the condensate with the steam can make the situation even worse. As long as the condensate stays inside the pipe, it will continue to affect in some form or other. Water hammer mechanism has been studied using CFD simulation analysis to suggest a solution for CIWH.

This paper focused on simulating the phenomenon of CIWH. This paper investigates the actual CIWH event in EPC industry as an example, and the study was conducted to find the root cause of water hammering. CIWH occurred due to condensate generation during start up with the boiler going into trip condition. The loading due to hammering caused damage to the vulnerable pipe branch and support. A simple pipe system has been modelled to simulate the typical phenomenon of CIWH with a pump and valve system has been included.

The results showed that piping geometry and operating conditions both acts as a condition that caused the CIWH. Gradual warm up and pressurization during startup and inclining the pipe downward in the direction of steam flow can be a way to prevent from CIWH in design stage. Additionally, operation for opening of the isolation valve shall be carefully monitored during the start up process.