Flow generated by a disc turbine in aqueous solutions of polyacrylamide

Abstract

The flow generated by a disc turbine in aqueous solutions of polyacrylamide (PAA) (molecular weight: 5 × 10⁶-6 × 10⁶) in a cylindrical tank was measured using laser Doppler anemometry. The tank diameter was 300 mm, with a flat bottom and provided with four T/10 baffles. The disc turbine was 100 mm in diameter and was centrally located. The liquid height was kept equal to the vessel diameter. The effect of polymer concentration on the flow was investigated for the same impeller speed. Results obtained were compared with those where only water was used as the flow medium. The effect of the impeller speed was also investigated for a polymer concentration of 5000 ppm. Dimensionless mean velocities were found to be independent of the impeller speed in the impeller vicinity. The primary, secondary flow numbers and power numbers decreased with an increase in the polymer concentration. The values of maximum shear rates were estimated in the impeller region as well as bulk region. On this basis, Reynolds number have been reported. They were found to be in qualitative agreement with the Reynolds number obtained by Metzner-Otto correlation. A procedure has been given for the estimation of turbulent energy dissipation rate. A complete energy balance has been established for the case of turbulent flow. The turbulent energy dissipation rates were also determined for the polymer solutions where the flow was in the transition regime.