Abstract Summary (Max 250 words)
In various mixing operations in tanks, achieving good mixing without an impeller is sometimes necessary. These include cases, such as metallurgical applications where the liquid is a molten metal, and cases where an inhibitor has to be rapidly blended in to avoid a runaway reaction due to impeller failure. In such cases, gas is often used to induce bulk flow and mix the contents of the tank. The present study investigated the use of gas to induce mixing in tanks without impellers by measuring the liquid phase mixing time using a decolourisation technique. In all cases the gas was introduced using a vertical dip pipe from the top of the tank. Experiments were conducted at three different scales, using tanks with diameters of 0.45, 0.61 and 1 m (roughly 67, 160, and 730 litres, respectively), all un-baffled and with torispherical bases. The effects of the off-bottom clearance and eccentricity of the dip pipe were quantified, as well as that of the gas flow rate, using air and water as test fluids. The effect of liquid height in the tank was also examined, and preliminary work has been carried out on the effect of viscosity using glucose solutions. It has been found that gas injection is an effective method for mixing liquids. The mixing time reduces as the power input due to the buoyancy of the gas increases, though scale, geometric parameters, and liquid viscosity can have a significant effect. Different scaling parameters and correlation approaches have been assessed.
