Numerical simulation of water hammer induced by steam direct contact condensatio in a horizontal pipe

摘要

Contact of steam and sub-cooled water in a pipe or a pressurized vessel leads to intensive condensation accompanied by a pressure drop in the volume of condensing steam and an acceleration of the surrounding water mass towards the steam volume, which can result in a severe water hammer and plant damage.This phenomenon is known as condensation induced water hammer (CIWH).The present paper aims to investigate the CIWH phenomenon with the computational fluid dynamics (CFD).Condensation of saturated steam on the cold water which is slowly flooding the horizontal pipe is numerically simulated.The Volume of Fluid (VOF) two-phase flow model and Large Eddy Simulation (LES) turbulent flow model of FLUENT have been used.Also, a thermal equilibrium model considering heat and mass transfer was introduced to model steam condensation using user-defined function (UDF).The experiments of condensation induced water hammer were performed in the PMK-2 facility------a full pressure thermo-hydraulic model of the primary loop of the VVER-440/312 type nuclear power plant and the simulation have been done on CFX platform by Luka (S)trubelj and Iztok Tiselj [1].Their simulations quantitatively captured the some phenomena of the experiments.We analyzed the characteristic parameters of the flow field, such as temperature, heat transfer coefficient and steam condensation rate.However, they cannot observe condensation induced water hammer.In our current work, we are using the commercial software to repeat this simulation.Our numerical simulation results clearly show the phenomena of the experiments.Particularly important is that we observe condensation induced water hammer.However, because of the stochastic nature of the particular condensation induced water hammer, we cannot predict the time and position of the slug formation in the pipe.Additionally, the pressure peak value we calculated is larger than the pressure peak in the experiment.In the subsequent work we will improve the numerical model to get a relatively accurate pressure peak.