Experimental Investigation on the Effects of a Spacer Grid on Single- and Two-Phase Flows

Experiments are performed in a scaled 1x3 rod bundle adiabatic air-water test facility to investigate the effects of a spacer grid on singleand two-phase flows. A four-sensor conductivity probe is used to obtain detailed measurements of local time-averaged two-phase flow parameters, including the void fraction and interfacial area concentration, throughout the flow cross-section at four axial locations. The local two-phase flow data indicates that the spacer grid causes redistribution of the bubbles. In the transition from bubbly to slug flows, the spacer grid is found to promote bubble coalescence. In the slug to churn-turbulent transition, however, the grid breaks up the larger bubbles, causing an increase in the interfacial area concentration across the spacer grid. Additionally, local velocity measurements in single-phase liquid flow are performed with a laser Doppler anemometer to investigate the change in the turbulence structure across the grid. The axial turbulence intensity measurements show the influence of the spacer grid dimples, indicating an increased mixing effect from these structures.