Two-Phase Flow Visualization and Pressure Drop of Air-Water Flow in a Horizontal 7-Rod Bundle

Abstract

Accurate physical descriptions of coolant voiding phenomena and two-phase flow in horizontal bundles are important to the safety of CANDU nuclear power plants. This paper presents adiabatic air-water experiments that were performed in a horizontal 7-rod bundle string to investigate two-phase flow regimes and pressure drop under low-flow conditions where limited data exists. A total of 235 air-water flow combinations were tested, ranging from 0.1 – 4.5 m/s liquid superficial velocity, and 0 – 4 m/s gas superficial velocity. Digital cameras installed 1/3rd of the distance from the bundle end, were used to record over 25,000 images of two-phase flow patterns. A flow pattern map was developed to identify flow regime boundaries, which included elongated bubbly, plug, slug, and froth. Corresponding pressure-drop data of selected flow conditions are also presented. These measurements enhance the understanding of flow-regime behaviours at low flow, and will help guide future experiments to study the flow regimes in the sub-channels.