Condensation Induced Water Hammer is a rapid condensation event. It could also be aptly termed a rapid steam bubble collapse. It occurs when a steam pocket becomes totally entrapped in sub-cooled condensate. As the trapped steam gives up its heat to the surrounding condensate and pipe walls, the steam changes from a vapour to liquid state. As a liquid, the volume formerly occupied by the steam shrinks by a factor ranging from several hundred to over a thousand, depending on the saturated steam pressure. Likewise, the pressure in the void drops to the saturated vapour pressure of the surrounding condensate. (For example, the saturated vapour pressure of condensate at ambient temperature is less than 1 psia). This leaves a low pressure void in the space formally occupied by the steam. The surrounding condensate still under steam pressure will rush in to fill the void. The resulting collision of condensate generates an over-pressurisation that reverberates throughout the section of pipeline filled with condensate. Since condensate is virtually incompressible, in a collision, it does not give. (Source: www.hse.gov.uk/)
Related Definitions in the Project: The Process Engineering; Operation and Maintenance
