Investigation on cross-flow characteristics of two different mixing vane grid in a 5 x 5 rod bundle

To comprehend the combined mixing effects downstream two different MVGs installed at same axial height, individual analysis of these MVGs is the precondition. In this paper, an experimental study on the crossflow distribution downstream two different split-type MVGs is presented by PIV in a 5 x 5 rod bundle. The cross flow in the sixteen inner subchannels is obtained at elevation from 1.8 D-h to 25 D-h downstream grids. For both two types of grids, two individual co-rotating vortices are observed near the grid in each subchannel and inter-subchannel cross flow increases before approximate 3 D-h and decays exponentially. The secondary-flow and cross-flow intensity of grid type I overweigh the type II and the intensities are corelated to horizontal projected area of vane. Based on the experimental results, an improved subchannel mixing grid model is proposed and the predicted cross flow in the gap is in good agreement with measured results.