Common Mixing Terminology
Axial Flow
Flow of fluid that runs parallel to the axis of the mixer shaft. If the flow moves away from the drive unit, it is considered "down pumping". Flow moving toward the drive unit is considered "up pumping".
Baffles
Solid surfaces placed in the path of the fluid flow generated by the impeller. Often placed against the walls in round tanks, these surfaces help to prevent vortexing and enhance vertical turnover in the tank.
Bulk Fluid Velocity (BFV)
(Ratio) The cross sectional area of the vessel divided by the pumping rate in a tank with a 1:1 aspect ratio. Useful calculation of the level of agitation in the tank.
Coverage
The distance between the impeller and the surface of the fluid. Coverage is necessary to prevent vortexing. In most applications, the minimum desired level of coverage is two times the impeller diameter (D), Min Desired Coverage = 2D.
Critical Speed
The natural frequency of vibration of the mixing system is called Critical Speed. When operated near this speed, the vibrations in the system can cause extreme shaft deflection and/or failure. Mixing systems should not be designed to operate at speeds near the Critical Speed or its harmonics.
D (variable)
(Ratio) The relationship between the Impeller Diameter (D) and the Tank Diameter (T). Testing has shown that as viscosity increases, the D/T ratio must also increase for optimal mixing.
D/T
(Ratio) The relationship between the Impeller Diameter (D) and the Tank Diameter (T). Testing has shown that as viscosity increases, the D/T ratio must also increase for optimal mixing.
Flow
A measurement of the movement generated in the fluid being mixed. The pumping rate of the rotating impeller is usually regarded as a measurement of flow. Applications with high flow exhibit rapid turnover of the material, but low levels of Shear. Generally, shear and flow are inversely related.
Flow Number (Nq)
The Flow Number is a measurement of the pumping capacity of a specific impeller design.
FMB (acronym)
Acronym: From Mounting Base. Used to specify the location of the impeller relative to the base of the mount. Determines required mixer shaft length.
Freeboard
The distance from the surface of the fluid to the top of the tank or vessel. Adding the Freeboard to the Coverage is useful in determining the proper shaft length of a mixer.
Impeller
The device which actually contacts the fluid and accomplishes mixing. A wide array of standard designs exist with specific flow and shear characteristics desirable for different applications.
Power Number (Np)
The Power Number (Np) is a constant, specific to each impeller design, that represents the power requirements for the use of that impeller.
Off Bottom
The distance between the mixing impeller and the bottom of the tank. In most applications, the desired Off Bottom distance is one to two times the impeller diameter (D), so in some applications, Optimal Off Bottom = D.
Pumping Rate (Q)
Measurement of the actual flow rate generated by a specific impeller rotating at a known speed. Usually measured in gallons/minute or liters/minute.
Radial Flow
Flow of fluid that runs perpendicular to the axis of the mixer shaft. Radial flow impeller generally move fluid from above and/or below the impeller and pump them outward to the walls of the tank where the material is diverted up and/or down along the wall.
Reynolds Number
A dimensionless number that represents the magnitude of fluid motion or agitation generated in a mixing application. This number is used in calculating the flow and power draw in applications with viscosity levels higher than water.
Service Factor (SF)
A measurement that suggests a lifespan adjustment to the expectations of a mechanical system. For example, if a gearbox which has a 1.0 SF rating under constant use with a 5HP motor is actually used in a system with a 2.5HP motor under constant use, the gearbox has a service factor of 2.0 suggesting that the expected lifespan of the gearbox has been substantially increased because it is being underutilized in the current configuration. In general terms, a system with a Service Factor less than 1 is overstressed and will fail prematurely, while a system with a Service Factor greater than 1 is underutilized and will last longer than expected. Typically, mixer gearboxes should be designed with a service factor of 1.5 or greater.
Settling Rate
The terminal velocity of the particles falling through the fluid, usually measured in feet/minute or meters/minute.
Shear
A measurement of the stress produced on the fluid being mixed. Applications with high shear have areas where neighboring particles have significantly different velocities causing the intermixing of fluids, dispersing of gases, or breakdown of the cohesiveness of liquid droplets. Generally, Shear and Flow are inversely related.
Viscosity
A measurement of the "thickness" of a fluid. Usually measured in CentiPoise (Cp), this "thickness" is actually a measurement of the internal fluid friction (resistance to motion) of the fluid.
Vortexing
Typically undesirable, this rapid swirling of the fluid pulls the fluid surface down around the shaft until the surface contacts the impeller, which allows ambient air to become part of the mix. Vortexing substantially reduces the life of the mixer and does not promote good mixing.
Mixing Types
Air Drive Mixer
A mixer powered by pneumatic motor, which uses a compressed air supply instead of electricity to generate motion.
Direct Drive Mixer
A mixer designed such that the speed of the mixer shaft matches the speed of the motor shaft. This simple design is often accomplished by using a simple coupling to attach the two shafts together. Some Direct Drive mixers incorporate bearing support to provide additional mixer shaft stability. Direct Drive mixers tend to generate higher levels of shear, but have lower levels of pumping efficiency.
Disperser
A disperser is a high-shear mixer (or sometimes just a high-shear impeller) designed to break up and blend particles or powders to generate a finer-grained mixture. The Cowles or "Sawblade" impeller is a typical dispersion blade.
Drum Mixer
A mixer specifically designed to mix or agitate drums of material, Drum mixers are usually permanently mounted to a special lid or through a standard 2" NPT bung hole. Drum mixers typically incorporate folding drum impellers which allow the impeller and shaft to be inserted and retracted through the entry hole of the vessel to be mixed.
Gear Drive Mixer
A mixer designed such that the speed of the mixer shaft is lower than the speed of the motor shaft through the insertion of a reducing gearbox between the motor shaft and the mixer shaft. Some Gear Drive mixers incorporate bearing support to provide additional mixer shaft stability. Gear Drive mixers tend to generate high pumping efficiency, but lower levels of shear.
Homogenizer
In mixing circles, a Homogenizer is a mixer that generates intensive blending through the use of very high speeds to create creams or emulsions from materials that tend to be incompatible (like mixing oil and water).
Parallel Shaft Mixer
A Gear Drive mixer designed such that the axis of rotation of the mixer shaft is oriented parallel but not collinear to the axis of rotation of the motor shaft through the insertion of a parallel shaft gearbox between the motor shaft and the mixer shaft. Parallel Shaft Mixers are typically chosen where an economical, higher quality gearbox is required and the additional length of the drive unit is not prohibitive. Parallel angle gearboxes typically utilized simple gear arrangements to generate the reduction in shaft speed. Some Parallel Shaft Mixers incorporate bearing support to provide additional mixer shaft stability. Because Parallel Shaft Mixers are also Gear Drive mixers, they tend to generate high pumping efficiency, but lower levels of shear. Fusion Fluid Equipment offers Parallel Shaft Mixers within their Flow Series Product Line.
Pharmaceutical Mixer
A mixer specially designed to address the sanitary requirements of the application. Pharmaceutical mixers are commonly made from stainless steel components with various forms of polish or surface treatments to support proper sanitation and cleanup. They are usually used in closed tank applications and contain seals to prevent contamination by maintaining the integrity of the mixing vessel.
Portable Mixer
A mixer specifically designed to enhance portability from mixing vessel to mixing vessel. Portable mixers usually utilize a c-clamp or cup plate mount to allow quick and easy movement and adjustment in open tank applications. Stainless steel portable mixers are also available at Fusion.
Right-Angle Mixer
A Gear Drive mixer designed such that the axis of rotation of the mixer shaft is oriented at a right angle (90°) to the axis of rotation of the motor shaft through the insertion of a right angle gearbox between the motor shaft and the mixer shaft. Right-Angle Mixers are usually chosen to address economic, environmental and logistical issues like cost constraints, equipment utilization, or limited clearance/accessibility. Right angle gearboxes typically utilize worm or helical-based gear arrangements to accomplish the change in direction and reduction in shaft speed. Worm drives tend to be more economically friendly, but lack the quality and high service factor of a helical-based gear arrangement. Some Right-Angle Mixers incorporate bearing support to provide additional mixer shaft stability. Because Right-Angle Mixers are also Gear Drive mixers, they tend to generate high pumping efficiency, but lower levels of shear. Fusion Fluid Equipment offers Right Angle Mixers within their Flow Series Product Line.
Sanitary Mixer
A mixer specially designed to address sanitary requirements of the application. Sanitary mixers are commonly used in the Pharmaceutical, Food and Beverage, and Chemical Processing Industries, or where corrosive conditions exist. Sanitary mixers are commonly made from stainless steel with various forms of polish or surface treatments to support proper sanitation and cleanup. They are usually used in closed tank applications and contain seals to prevent contamination by maintaining the integrity of the mixing vessel.
Side-Entry Mixer
Side-Entry mixers enter the mixing vessel through the side wall of the vessel. Side-Entry mixers usually mount via an ANSI Flange or TriClamp Flange and incorporate integral seals to prevent materials from escaping the tank through the mixer.
Static Mixer
Static mixers are tubes or pipes that contain stationary devices designed to use the kinetic flow of the material to accomplish mixing or blending. Browse and buy online at Volcrest.com, a division of Fusion Fluid Equipment LLC.
Top-Entry Mixer
Top-Entry mixers enter the mixing vessel through the top. Top-Entry mixers can be configured for open or closed tank configurations as required by the application.
Tote Mixer
A mixer specifically to mix or agitate totes of material. Tote mixers are usually mounted across the top rails of the tote with a "bridge" or through the tote cap. Tote mixers typically incorporate folding tote impellers which allow the impeller and shaft to be inserted and retracted through the entry hole of the vessel to be mixed.