Flow visualization in a vortex tube by using a tuft method

In this paper, the flow of a counter flow type vortex tube is visualized. The flow visualization is performed by means of the tuft stick method. The tuft dyed with fluorescent dyes is used and the length of the tuft is changed from 5mm to 20mm at intervals of 5mm.The obtained results are summarized as follows;1) It is considered that, except for near the wall, the tuft with 5mm length only shows the direction of flow but does not show the actual inner flow because of the stiffness of a thread.2) If the tuft with over 10mm assumes to show a phenomenon close to the real inner flow, it will be supposed that those tufts present a secondary flow in the vortex tube.