TURBULENT PROPERTIES IN BUBBLE-FLOW REGION IN EXTERNAL-LOOP AIRLIFT BUBBLE COLUMN

概要

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Turbulent properties of the bubble flow region in an airlift bubble column were examined using an anemometer for water and CMC solutions. The turbulent structures of the gas-liquid system in these liquids were evaluated by the power spectrum of turbulent eddies. The power spectrums of the liquids decayed with decrease in the size of eddies with a slope of –5/3 to –2. This is almost comparable to that of Kolmogoroff’s spectrum law for an isotropic turbulence. The radial distributions of turbulent intensity, u′l, macro-scale of turbulent eddies, Λf, bubble diameter, dB, and bubble rise velocity, uB, were measured. The influence of the media on these properties was examined. The turbulent viscosity, νt, was evaluated from the values of u′l, and Λf for the liquids. It was found that νt of gas-liquid two-phase flow was five times higher than that of a single-phase flow of water. Using these turbulent properties, the liquid superficial velocity, UL, slip velocity of bubble, uBS, and bubble diameter (Sauter diameter), dBS, in the riser were estimated theoretically. The estimated values agreed with those obtained experimentally.
1993-12-01