Average liquid film thickness of annular air-water two-phase flow in 8 × 8 rod bundle

In order to develop detailed model of the annular two-phase flow the average liquid film thickness is an important parameter. It can significantly affect the occurrence of dryout and post-dryout phenomenon on heater surfaces. Most research on film thickness has been focused on pipe flows. Data in rod bundle geometry are very limited. However data in rod bundle geometry is much more valuable for reactor safety modeling and calculations. Because of this, an experiment to measure liquid film thickness has been performed for the air-water annular flow in a 8 × 8 BWR rod bundle. Film thickness data were obtained both on the rods and on the channel wall. Data were recorded at four axial locations within the rod bundle. This included locations just before and just after a spacer grid. This allowed the spacer grids effect on the film thickness to be evaluated. The minimum film thickness was on the center rod. Also, the presence of the spacer grid resulted in reduced film thickness.