Impeller technology has improved in leaps and bounds in recent years, with manufacturers now able to select the precise impeller needed for almost every imaginable mixing requirement.
Choosing the right impeller can have a positive effect on product quality, consistency and product yield. Impellers selected with care and precision can vastly improve the overall mixing process, however, the reverse is also true: an impeller that is not fit for purpose is likely to deliver inconsistent results, increase the cost per batch and even negatively affect equipment uptime.
It’s vital for manufacturers to consider the knock-on effects of the wrong impeller for the job, and ensure that the mixing process is fully optimised in order to maintain an efficient operation.
The dangers of not optimising your mixing process
The success of a fluid mixing process is often measured by the quality of the end result. Thorough coalescence and amalgamation of ingredients into the desired consistency is the benchmark by which QA teams measure the validity of the product. So, if mixing results are inconsistent, rejected batches are more likely to occur which pushes up costs and produces unnecessary waste.
If your mixer and impeller combination is unable to deliver the necessary torque, speed and shear properties, you run the risk of slowing down your production process and negatively impacting your cost per batch. Likewise, an impeller that is over-engineered for the task will be using excess energy and contributing to unnecessary wear on the mixer.
Correct sizing matters too – an impeller that is larger than necessary means a larger shaft and drive is required, increasing equipment costs. A too-small impeller will require longer operation time and more energy to operate.
The good news is that cost increases, production time blowouts and unnecessary waste are all preventable. An optimised mixing process starts with choosing the right impeller for your needs based on the unique balance of flow, pressure and shear forces required.
Which impeller is best for my process?
Axial Flow Impellers
Axial flow impellers are best for blending and suspension tasks and suit low viscosity products, such as those typically in food and beverage mixing applications.
The flow pattern has a strong axial suction and bundled discharge stream in the turbulent flow range. The outlet jet stream is deflected at the bottom and reaches the surface in the wall area of the vessel, whilst the liquid is accelerated in the propellor zone.
Products such as the Mixquip Superflo Propellor are very effective at low viscosity / high flow mixing at higher shaft speeds. This stainless steel impeller design has a low power number and high pumping capacity.
Mixquip’s Hydromax Impeller is another example of an axial flow-based mixing system that covers both turbulent, low viscosity mixing regimes, as well as positive displacement mixing in laminar, high viscosity regimes. With a sharper blade than the curved profile of the Propellor type, this versatile impeller allows for adjustments to the blade angle and the ratio between the tank and impeller diameters, making it very versatile.
Radial Flow Impellers
Radial impellers are used with a range of viscosity media and are excellent for gas / liquid mixing and dispersion duties. The flow pattern is ideal for low-level mixing, creating an acceleration in the liquid via centripetal force outwards of the propellor zone. When the flow meets the tank wall it is directed both upward and downwards to create effective mix patterns and movement.
Radial flow impellers are ideal for applications such as wine, food and beverages, water treatment and mining applications.
Mixquip’s Radial Blade is best for high-intensity mixing applications where gas dispersion or solids suspension is required. Depending on your tank geometry, multiple impellers may be required as the mixing effect occurs in the shear zone of the radial outflow.
High Shear Disperser Blades are used for fine grinding of solids and are effective at dispersing difficult pigments. The high rotational speeds of this impeller force the product outward over the blade to the teeth, where solids are broken into increasingly smaller particles.
Tangential Impellers
Mixquip Gate Style Impellers are typically used with highly viscous materials and in the laminar flow range to disrupt the boundary layer adhering to the vessel walls where heat transfer is required in both heating/cooling applications.
Fingers or frames can be added to increase the versatility of these impellers, or combined with axial/radial blades as a counter-rotating mixing system.
Axial/Radial Impellers
These combined flow impellers are used for both axial and radial liquid movement and are suitable for use with non-Newtonian fluids covering a wide range of viscosities.
The impellers create strong fluid flow patterns which are deflected at both the wall and the bottom of the tank. This combined flow action is ideal for mixing in the transitional and laminar zones. Impellers such as the Torojet and the Pitched Blade Turbine are recommended for axial/radial flow requirements for applications such as water treatment, paint and other industrial mixes.
The Torojet excels at producing a flow pattern through the entire vessel without any dead zones. The PBT is suited to low to medium viscosity applications where axial flow is preferred and a degree of shear is beneficial to the overall process result. This design is ideal for breaking agglomerates and distributing solids within the mixing vessel.
High Shear Impellers
Mixquip’s high shear impellers are suitable for blending and homogenization of liquids of greatly varying viscosities. They are also ideal for the disintegration of solid and semi-solid materials in industrial, oil and lubricant industries, as well as some food and beverage applications.
The high shear work heads come in various profiles and are well suited to rapid size reduction of soluble and insoluble solids. The solution is dispersed through the mixer head at a great force causing consistent agglomerate-free results. High shear stator impellers are available from Mixquip in various designs including high flow, two-stage, and multipurpose variants.
Advice on optimising your mixing process
The Mixquip team is on hand to provide technical advice and support on impeller selection, performance, and the efficiency of your entire mixing process.
Combining strong industry knowledge with the best technology for over 50 years, our engineering team works to fully understand your mixing challenges and provide comprehensive solutions. Contact us today for more information.
