Flibe blanket, which uses molten salt Flibe as coolant and tritium breeder, is considered as one of the candidates of advanced liquid blanket for fusion reactors. Although Flibe has low heat transfer performance which comes from high Pr, sufficient heat removal can be achievable by using sphere-packed pipe (SPP) as heat transfer promoter. In this study, heat transfer correlations of SPP which can be available for high Pr fluids are derived from experimental analysis inserting various size and materials of spheres into the pipe. Further, heat transfer performance in a rectangular channel is simulated by using sphere-packed annular channel. Based on these results, heat transfer performance of Flibe blanket is evaluated and some design window with pressure drop of less than 1 MPa/m was confirmed.