Abstract
Mixing of liquids in tanks by means of a non-reacting gas-bubble plume was studied by using a tracer response method. The circulation time was obtained from the period of a damping oscillation of the response curve. The mixing time was defined as the time required to reduce the concentration variation to within 1% of the mixed mean value and was measured by an impulse response.
The results indicate that the induced liquid flow-rate varies as the first power of the submergence depth of the nozzle and as the 1/3 power of both the gas flow rate and the horizontal cross-section of the tank. When the circulating flow in the tank dominates the mixing, the ratio of mixing time to circulation time is nearly equal to that of the liquid jet mixing, and increases with decreasing distance between nozzle and side wall of the tank. When gas is injected in a central region of the tank, the mixing time becomes larger with decreasing depth of liquid, due to an effect of relative stagnation. Rapid mixing is achieved by injecting gas at a mid-radius of the tank, where the effects of both tank wall and relative stagnation can be excluded.
