EMI, Inc. is a Connecticut based manufacturer of both portable and fixed entry process mixers and agitators. Founded in 1982, EMI, Inc. entered the market by its acquisition of the "Eastern" Mixer product line from the LFE Corporation. EMI's product offering expanded considerably after its second acquisition, the "Cleveland" Mixer line from Greerco in 1984. Both of these product lines date their origins to the mid 1940s.
As technologically advanced as any mixer manufacturer on the market, EMI, Inc. helped pioneer the development of both hydrofoil impeller technology and the cartridge seal with shaft catcher designs now common place for large, over-hung shaft designs. With an experienced engineering staff behind them, EMI, Inc. offers a full performance guarantee for all of their products when selections for specific applications are made by EMI, Inc. engineers.
EMI, Inc.'s publication, Agitation Design Guidelines and Fundamentals, makes an excellent reference document for interested engineers with little or no mixer / agitator experience. This publication contains all of the basics, including tips on tank design, the application of tank baffles, the relationships between Reynolds numbers and power draw and pumping efficiency, primary flow, bulk velocities, shaft design, and impeller designs.
Also available are a number of published technical papers written around process specific applications, e.g. The Application of Fluid Mixers
- in Water & Waste Treatment, which includes basic process criteria, carbon slurries, lime slurries, batch make-up of treating chemicals, rapid mixers, and flocculators,
- for Polymerization,
- in the Pulp & Paper Industry, which includes process specific criteria, clay make-down, coatings blending, coating storage, pigment adhesive binding, and starch cooking,
- in the Paints & Coatings Industry.
Mixer Impellers
A mixer is any mixing element which is driven by auxiliary equipment, such as shaft, speed reducer, and electric motor to provide mixing action.
Mixers are generally categorized by the flow pattern they produce relative to the shaft centerline or the impeller axis in a fully baffled tank. Further, breakdown is based on relative shear produced. The resulting divisions are: axial flow, radial flow, hi-shear, low-shear or high flow and specialized impellers (those which are normally used in unbaffled tanks).
The primary types of axial flow impellers (see Fig.1 ) are the propeller, the pitched blade turbine, and the hydrofoil designs. The propeller is restricted to small mixers because of its weight. The pitched blade is used when a balance of flow and shear is required. The hydrofoil offers the best high flow design. All are built with cast hubs and bolted blades in larger sizes.
The flow pattern produced by a typical axial flow impeller is shown in Fig. 2. When the vessel is fully baffled and the agitator is center mounted, excellent top to bottom motion is produced resulting in good mixing (see Fig. 2B). If the baffles are removed (Fig. 2A), swirling and vortexing result, mixing becomes very poor and the hydraulic forces on the impeller increase dramatically. The flow pattern can be improved by moving the agitator off center (Fig. 2C). This will restore most of the top to bottom motion; however, the hydraulic side forces remain high and if the impeller passes very close to the wall, the force may become cyclic.
Choosing from a wide variety of impeller designs, EMI, Inc. is capable of specifying and offering an engineered solution for most any mixing, blending, or agitation service, limited only by horsepower and/or over-hung shaft. Following are a few of the more common impeller designs offered and applied with "Cleveland" Mixers:
XTF-3 and XTF-4 impellers represent the ultimate in hydrofoil technology. These three and four blade impellers capitalize on the understanding of lift and drag properties of hydrofoils, allowing the maximum in true axial flow performance, at the same time minimizing localized turbulence and flow separation, all at substantial energy savings.
AXF-4 is a four blade, 45 degree axial flow turbine, which for many years has been used for flow controlled applications. With low Reynolds numbers, the AXF-4 also offers a high flow regime at low RPM without the drag associated with older, radial designed impellers.
The three bladed marine propeller still sees plenty of service, as well, especially for fixed speed services, small tank capacities, and relatively thin fluids where the introduction of shear is not a constraint.
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