Flow visualization experiment of a swirling flow formed downstream of a piping with successive three elbow to be applied to Divertor cooling

As one of potential divertor cooling systems, threedimensionally connected elbow piping has been proposed. In this study, a visualization experiment was conducted for swirling flows generated downstream of five kinds of piping with successive three three-dimensionally connected elbows in order to evaluate the applicability of these systems to divertor cooling by comparing with the dual elbow case previously obtained in terms of strength of the swirling flow and turbulent statistics. From the experimental results, it was found that the triple elbow piping in which all elbows were connected three- dimensionally, referred to as 3D+3D layout, generated strong swirling velocity components than those of the dual elbow case and it became up to 70 % of the mean flow velocity. Moreover, it did not attenuate even 5D downstream of the triple elbow, where D was the diameter of the piping and the applicability of this flow field to divertor cooling can be promising. In addition, when heat transfer was evaluated in terms of turbulent statistics in the 3D+3D layout, heat transfer enhancement is expected because larger turbulent kinetic energy was observed near the pipe wall than a straight piping case.