Unsteady mass transfer in turbulent flow close to a rotating cylinder

Electrodiffusional methods of studying unsteady turbulent mass transfer involved measurement of a transient current characteristicI() after step polarization of a rotating annular cylindrical 46 mm dia electrode at a fixed rotational velocity atRe=(2–9)×10⁴ andSc=2.4×10³. The potassium ferri-ferrocyanide system with NaOH background electrolyte was used. An initial asymptote at 0 served as a test. The similarity of the normalized transfer coefficientK₊=/u_* with respect to the Reynolds number demonstrated turbulent flow development. Tests were aimed at determining the powern in the approximate law of attenuation of turbulent diffusionD_t in they-direction normal to the wallD_t/v=by₊ⁿ.A numerical solution of the unsteady turbulent diffusion equation obtained as a set of lg ()=f() curves for 3n4 with an interval 0.2, where ()=I/I()_#x2212;1 has been achieved.Notation I diffusion current - C C₀ andC_p concentration, concentration in the bulk liquid and polymer concentration, respectively - C_f drag of a Newtonian fluid - time - U linear velocity - v kinematic viscosity - angular velocity - j flow - y₊ yu_*/v, ₊ = u_*² and=(1-C/C₀), dimensionless quantitiesThis paper was presented at the Workshop on Electrodiffusion Flow Diagnostics, CHISA, Prague, August 1990.