Development and Validation of Pattern Recognition Algorithm and Suppression Pool Flow Modelling

Abstract

The comprehensive understanding of the dynamics of vapour bubbles and jets discharged from vent pipes and spargers into subcooled liquid has a significant role in assessing the capability of nuclear safety systems to perform their function properly. However, high-resolution local measurements and numerical calculations of these complex and rapidly condensing gas volumes are challenging due to rapid pressure oscillations, microscopic length, and time scales of turbulent two-phase flow. Visual observation of the interior of test section can make modern measurement techniques a viable alternative in such cases.

This paper presents the work concerning the modelling of vertical (vent) and horizontal (sparger) steam injection in a water pool by applying the Eulerian-Eulerian two-fluid approach. In this work, the formation and collapse of the steam bubbles in chugging condensation mode and bubbling condensation oscillation mode are evaluated by using pattern recognition (PR) algorithm. The PR algorithm is based on video material recorded during the direct contact condensation (DCC) experiments of PPOOLEX and SEF-POOL test facilities. The velocity of collapsing bubbles is estimated with the PR algorithm. The accuracy of PR algorithm is cross-checked with the CFD simulation results. Results indicate that the presented PR algorithms provide important information on the dynamics of phase interface in all directions. These details are advantageous for comprehensive DCC and steam-water surface instability model development. Results show that inclusion of interfacial instability modelling i.e., the Rayleigh-Taylor interfacial area model in Eulerian two-fluid simulation, inevitably improved the interface roughness and thereby heat transfer, which controls bubble growth and collapses.