Using a recirculation loop for mixing is unpredictable in all cases.
 
1) For mixing a small batch, recirculation may work or may not, depending on the degree of mixing required.  Mixing with a recirculation loop may work if minimal or poor mixing is adequate.  Vigorous mixing with a high degree of uniformity is probably not possible with a recirculation loop.  The flow location and velocity returning to the vessel will dictate the degree of uniformity possible and is unpredictable.  In all cases, bulk uniformity will be more difficult to achieve with a recirculation loop than with a well designed mixer.
 
2) If impeller mixing if not desired because of high shear, then a recirculation loop is even less desirable.  A typical centrifugal pump used in a recirculation loop will create five to ten times the shear of an impeller mixer.

The simple answer concerning the use of a recirculation loop is try it and if it works, use it.  If it does not work for the required mixing, don't be surprised.  Mixing is too general to describe simply, even just for blending as both time and uniformity are involved.  A recirculation loop tends to create uniformity in some locations and not in others.


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