Editing Mixing (process engineering) (section)

==Liquid–gas mixing==
Liquids and gases are typically mixed to allow [[mass transfer]] to occur. For instance, in the case of [[air stripping]], gas is used to remove volatiles from a liquid. Typically, a [[packed column]] is used for this purpose, with the packing acting as a motionless mixer and the air pump providing the driving force. When a tank and impeller are used, the objective is typically to ensure that the gas bubbles remain in contact with the liquid for as long as possible. This is especially important if the gas is expensive, such as pure [[oxygen]], or diffuses slowly into the liquid. Mixing in a tank is also useful when a (relatively) slow chemical reaction is occurring in the liquid phase, and so the concentration difference in the thin layer near the bubble is close to that of the bulk. This reduces the driving force for mass transfer. If there is a (relatively) fast chemical reaction in the liquid phase, it is sometimes advantageous to disperse but not recirculate the gas bubbles, ensuring that they are in [[plug flow]] and can transfer mass more efficiently.{{Cn|date=March 2025}}

[[Rushton turbine]]s have been traditionally used to disperse gases into liquids, but newer options, such as the Smith turbine and Bakker turbine are becoming more prevalent.<ref>{{cite web |url=http://cercell.com/support/bactovessel-details/turbine-principles/ |title=Turbine principles |publisher=Cercell.com |access-date=2017-06-23 |url-status=live |archive-url=https://web.archive.org/web/20170611222544/http://cercell.com/support/bactovessel-details/turbine-principles |archive-date=11 June 2017 |df=dmy-all }}</ref>  One of the issues is that as the gas flow increases, more and more of the gas accumulates in the low pressure zones behind the impeller blades, which reduces the power drawn by the mixer (and therefore its effectiveness). Newer designs, such as the GDX impeller, have nearly eliminated this problem.{{Cn|date=March 2025}}