Mixer element: The element is the device that the fluid flows over or through that causes the fluid streams to blend.  Our most common elements are the BMV (Bartlett, mixer, vane) and the BMX (Bartlett, mixer, "X" style) elements.  See the descriptions of these elements below.  We offer removable and non-removable elements.  We almost always recommend removable elements because the additional cost for us is minimal, and a non-removable element should be considered to be not cleanable.

Mixer Housing: The unit which holds the mixing elements. We offer housings in any material in which pipe can be obtained (high nickel alloys, TFE lined, PVC, fiberglass) or some materials in which pipe cannot be purchased, but which can be fabricated from rolled and welded material.

Mixing efficiency: The common index of how well a mixer has mixed the entering flow streams.  It is usually written as "sigma over "x" bar".  Sigma refers to the standard deviation of the measured units of multiple samples collected at the downstream end of the mixer.  "X bar" refers to the proportion of the total stream that the smaller additive stream represents.  Although this unit can be used as a quick gauge of the throughness with which a mixer will mix two streams, the weakness of the mathematics must be kept in mind when two streams of nearly equal proportions are mixed.  As an example, when two equal streams are mixed the value of "x bar" is 0.5.  When a large standard deviation (sigma) is divided by a large "x bar" then a small (and ostensibly good) mixing efficiency number seems to be the result.  The value of the mixing efficiency can be misleading in instances of nealy equal quantities of the mixed streams.  A perfect example of this is an epoxy putty mixing applications where nearly equal flow rates are mixed.  As a result an unacceptably large variation in homogeneity would be hidden when it was divided by a large value of "x bar". In epoxy mixing applications the variation of the outlet stream needs to be more homogeneous than the typical mixing efficiency of 0.05.

Reynolds number: The ratio of the dynamic fluid forces to the viscous fluid forces.  Though the units of the numbers used do not literally compare the dynamic to the viscous forces of a fluid flowing through, over, or around an object, research data compiled using this formula allows the prediction of the velocity at which laminar flow ends and turbulent flow begins.

Turbulent flow: Fluid flow characterized by microscopic tumbling of a fluid as it flows.  This tumbling is why turbulent flow is most effective for mass or heat transfer.  Some mixing is achieved in turbulent flow.  To achieve the degree of mixing typically required, a length of pipe 100 diameters long or more could be required.

Laminar flow: Flow characterized by the sliding of fluid layers.  An example would be epoxy in a pipe at low velocity.  If a colored stream were added to this flowing epoxy, the colored stream would remain straight and in its location as the epoxy travelled down the pipe for many pipe diameters.  During laminar flow, heat transfer is primarily by conduction, and mass transfer is primarily by diffusion.  Both of these are very slow mechanisms.

Vane type element: The BMV element.  This element creates crossing flow channels that cause microscopic tumbling of the fluid between the two flow streams.  The mechanism which produces mixing is this tumbling which creates random trading of fluid from stream to stream.  In low viscosity applications, the BMV element produces the best mixing with the least pressure drop of any element design. 

"X" type element: The BMX element.  This element consists of crossed bars at an angle to the flow stream (i.e. an "X") which causes the flow stream to be cut and recombined.  At each cross section of the element, the flow stream is separated into 10 to 100 separate streams.  When compared to mixer elements which only separate the flow stream into two streams, it is easy to understand why the degree of mixing per element for the BMX is the best of any mixer available for laminar flow.  In laminar flow, pressure drop increases with every square inch of area over which the flow must travel.  Static mixers which require additional elements to achieve the same mixing effectiveness will have an increased pressure drop proportional to the additional metal area inserted into the flow stream.

We continue to add to this Static Mixer Glossary, but if you have questions which are not answered here, please call one of our Static Mixer Specialists for personal assistance.