Flow visualization and mixing quantification in a rod bundle using laser induced fluorescence

Laser induced fluorescence technique (LIF) was applied to visualize and quantitatively analyze fluid mixing in a fuel rod bundle geometry. A test facility has been designed and constructed at Harbin Engineering University (HEU) utilizing the matching index of refraction (MIR) approach. Single-phase experiments on the fluid mixing between subchannels were performed. Fluorescent dye tracer Rhodamine B (RhB) was injected in the sub-channels in the upstream of a spacer grid to visualize the fluid mixing process. Laser sheet was formed by optics system to emit the fluorescence, and a high-speed camera was used to record the fluorescence information to reconstitute the concentration distribution. The concentration contour maps were analyzed to illuminate the fluid mixing phenomenon in the rod bundle, and the influence of spacer grid was explored in detail. In addition, the coefficient of variation (COV) analysis was conducted to quantify the fluid mixing, and the phenomenon difference between the injection positions was investigated. The analysis results, which were in accordance with the previous studies, indicate that LIF technique is applicable in the study of flow inside rod bundle geometry. The whole-field measurement technique developed in this study is expected to provide a new insight on the research of flow inside fuel rod bundle geometry, which should be useful in the evaluation of CFD codes and spacer grid performance.