Experimental study of the features of the occurrence and development of condensation-induced water hammer in a horizontal pipe

Abstract

Condensation-induced water hammers (CIWHs) can occur in pipelines when saturated steam comes into direct contact with subcooled water, causing severe damage to related equipment and personal safety. An experimental study of the occurrence and development of CIWHs in a horizontal pipe is carried out at the special test facility developed in Electrogorsk Research and Development Center for NPP Safety. Subcooled water is supplied into the horizontal pipe filled with steam as a result of which CIWH may occur. The test facility has two novel features: 1) a damper cap to stabilize the water flow at the inlet part of the horizontal pipe and 2) a discharge vessel with closed drainage (during the experiment). The first feature allows us to study the effect of the water flow contraction at the inlet section of the pipe on the CIWHs occurrence. The second feature makes it possible to study CIWHs in various hydrodynamic conditions during the experiment. Four stages of the process are identified: 1) initial flow of water through a steam filled pipe; 2) free falling discharge of water; 3) filling the horizontal pipe; 4) filling the upper part of the discharge vessel. The features of the arising CIWHs at each stage are described. The main parameters affecting the occurrence of CIWH are the temperature and flow rate of the supplied water. An increase in water subcooling contributes to the CIWH probability and an increase in CIWH pressure peaks. CFD calculations reveal that at high flow rates of supplied water (3–5 t/h), strong disturbances develop on the interfacial surface due to the new mechanism of steam–water interaction under these conditions, which can contribute to the occurrence of water hammers. On the plane of parameters “water subcooling - Froude number”, a map of CIWHs based on the present study and other works, as well as the theoretical boundary of the occurrence of CIWHs, has been built. Our results shown on this map are in full agreement with the results of other researchers. It is found that in experiments performed under the same conditions, significantly different magnitudes of water hammers can be obtained, which is associated with the stochastic nature of this phenomenon. It has been revealed that the maximum magnitudes of water hammers are achieved when the horizontal pipe is half filled with water, and the area of the interfacial surface on which steam condenses occurs is maximum.