Author(s): K. Shiono; E. C. Teixeira

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Abstract: Turbulence measurements were undertaken using a two-component laser Doppler anemometer (LDA) in a serpentine contact tank (CT) commonly used for water chlorination. A detailed examination of turbulent parameters was carried out and showed the significant effects of the baffle lee and the inlet and outlet of the tank on the CT's hydraulic efficiency. Turbulence levels were quantified along the tank and were found to be considerably high in the tank inlet, first and second compartments and to be decaying rapidly in the latter compartments. The decay rate of turbulence along the tank is similar to that of the grid generated turbulence. The turbulence generation mechanisms in the first compartment were identified using comparative studies of the turbulence characteristics in the backward-facing step flow obtained by Eaton and Johnston (1981) and in the plane wall jet flow obtained by Rajaratnam (1976). The main contribution of the high turbulence level in the compartment was found to be due to shear generated turbulence in the upper layer. Tracer measurements were also carried out and an optimum dispersion coefficient at the outlet of the tank was found to be 16.2 cm2 . From the Marske and Boyle's equation (1973) in this tank, for b = 37, the dispersion coefficient is 2.9 cm2 , which is one order smaller than that obtained from this study.

DOI: https://doi.org/10.1080/00221680009498294

Year: 2000