MASS-TRANSFER TO LOCAL ELECTRODES AT WALL AND WALL FRICTION FACTOR INDECAYING TURBULENT SWIRL FLOW

This paper describes an investigation of mass transfer to local electr odes at the wall and wall friction factor behaviour in decaying swirl flow in a circular duct generated by short helical swirl generators. F ive swirl generators with angles between 15-70 degrees to duct axis we re employed. The experiments were carried out in a Reynolds number ran ge 8900-27 000 and at a Schmidt number of 1692. The axial distribution of the mass transfer to a circular electrode at the wall were measure d using an electrochemical technique and the friction factors at the w all were calculated. Flow visualization experiments showed that no cir culation nor dead zone occurs in the system. The local mass transfer d ata were correlated in the form of Sh(x) = 0.0490 Re-x(0.817) (1 + tan theta(0))(0.508) Sc-1/3 for the whole range of swirl generator angles and the following correlations were developed f = 0.2517 Re-x(-0.263) (1 + tan theta(0))(0.880) and f = 39.810 Re-x(-0.642) (1 + tan theta( 0))(0.746) for local friction factor for swirlers of 15-45 degrees and 60 and 70 degrees, respectively. (C) 1997 Elsevier Science Ltd.