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Mixing Guide >> Liquid Dispersion
Immiscible Fluids can be dispersed in a static mixer
operating in turbulent flow. This creates a solution of small
droplets of the dispersed phase in the continuous phase.
The use of static mixers allows for accurate prediction of drop sizes, which
can help with mass transfer calculations etc.
Dispersion can be considered as a mixing of two or more immiscible liquids
into a pseudo-homogeneous mass. Small droplets are created to provide contact
between the two phases. The reason for this can be to extract a solvent, to
remove or clarify color, to add or remove heat, or to affect mass transfer
rates. Common applications are to disperse water and hydrocarbons, and acidic or
alkaline solutions combined with organic liquids.
The term's dispersion and emulsion are often used interchangeably. However
for clarity, a dispersion is a term implying distribution, whereas an emulsion
is a special case of a dispersion where the resulting mix is relatively stable
with respect to time. A dispersion on the other hand is a 2 phase mixture in
which drops may coalesce. The material generally present in the larger quantity
is called the continuous phase, while the material formed into droplets is the
dispersed phase. The stability of an emulsion depends on the surface ion
activity which is a function of particle size (small particles have a larger
total surface). Small particles weigh less and so require less surface ions to
Turbulent conditions ensure a high intensity radial mixing action in a static
mixer. For proper dispersion calculations assume that turbulence will
develop at a Reynolds number of 5000.