Liquid Mixing and Agitation

What is Liquid Mixing and Agitation?

Where in the mixing process would you find Sterimixers and Sterivalves?

Numerous magnetic mixer designs can be found in upstream, downstream, and fill & finish applications. Our equipment excels particularly in aseptic liquid mixing applications including:

Solids are kept in suspension in a liquid phase. Low shear mixers are typically used. The amount of transferred power required depends on the particle settling velocity, the viscosity of the liquid, the percent solids and the degree of suspension that is desired (e.g. off-the-bottom or uniform).

Low shear mixers are used when the liquids are miscible. The pumping action of the mixer combines 2 or more liquids to create a homogeneous mixture in the tank. If the liquids are immiscible then, some degree of shear is required.  Quite often, a balance between flow and shear is used.

The liquid needs to be constantly moving in order to achieve a constant temperature in vessels with heating or cooling capabilities. A low shear mixer is used to circulate the liquid across the heat transfer surface.

Similar to mixing miscible liquids, the mixer pumping action helps to dissolve the solids. Floating solids often require the formation of a vortex plus some shear to be fully incorporated. Sinking solids must be suspended to be fully incorporated and some solids require shear to be incorporated. All solids will reach a saturation point, where no additional solids can be incorporated.

This is a common application in bioreactors, where a gas is introduced and the mixer disperses the bubbles to increase the oxygen transfer. The required degree of shear is related to the oxygen transfer rate required by the application.

The liquid is kept in constant movement using a low shear mixer in order to maintain homogeneity of the concentration and temperature of the liquid throughout the vessel. Typical storage applications in the biopharmaceutical industry are buffer and media hold.

High pumping, low shear impellers are used in general blending applications and where the product can easily be damaged, such as cell culture. Low pumping, high shear impellers are used to create emulsions and incorporate powders that tend to float or agglomerate.

Viscosity is a property of fluids that characterizes their resistance to flow. A higher viscosity fluid is more difficult to pump than a lower viscosity fluid, leading to longer blend times. Some fluids “act” less viscous when shear is applied to them, often referred to as the apparent viscosity of a fluid. Viscosity is a very important factor to consider when sizing a mixer.

A vortex is a flow pattern formed by the mixer for the purpose of drawing down solids that would otherwise float. In a great number of cases, a vortex is not desirable because it can result in air entrainment and incomplete mixing.

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