Abstract A flow visualization study was performed for the convex louver fin geometry. The visualization was achieved using dye in a 20:1 scale model with water as the fluid. The louver angle and fin pitch were varied to determine the conditions that produced maximum mixing and therefore are expected to produce maximum heat transfer. The mixing efficiency was described using a dye mixing angle. The Reynolds number based on louver length was varied from 400 to 3000. For most configurations, the mixing angle increased with Reynolds number. Louver angles of 19 and 24° were tested. For each value of fin pitch ( F p) to chevron height ( H), the larger louver angle resulted in a large mixing angle. F p/4 H = 1, 1.5, 2 and 3 were tested the F p/4 H = 1.5, producing the largest mixing angle. The separation structure produced by the convex louver geometry was also studied using flow visualization.