This is the fourth blog in our Industrial Mixing Basics series on mixing impellers. It focuses on high viscosity mixing impellers (i.e., laminar flow impellers). These include the double helix impellers and ProQuip Doubly-Pitched HiFlow™ impeller.
Laminar Flow Impellers
Blending high viscosity fluids generally requires a mixing impeller that operates effectively in a high viscosity/laminar flow regime. Laminar flow is a fluid flow characterized by long, smooth flow currents, mainly in the same direction as the bulk of the flow with little interaction between them. In a mixing system, these fluids have a calculated Reynolds number less than 2000 (Reference: Industrial Mixing Basics: What is Reynolds Number?). Typical laminar flow impellers include anchor impellers, gate impellers and double-helix impellers.
A double-helix impeller is commonly used to blend high viscosity fluids operating in a laminar flow regime. The helical ribbons in this impeller are designed for close wall clearance. They operate at relatively slow speeds rotating in a direction to create fluid movement up along the wall. The fluid returns down the center of the tank providing overall blending in the tank. There are many high viscosity polymer applications mixed with helix impellers with viscosities exceeding 500,000 cps.
The following video demonstrates the action of a high viscosity fluid with a double helix impeller. This is a 13.25” diameter vessel with a 12.5” diameter double helix impeller. The fluid viscosity is 10,000 cps. The helix is operating in a laminar flow regime. A colored dye is added to allow visualization of the blending with fluid flow up along the walls and down the center. The blend time for this high viscosity fluid is relatively short.
ProQuip Doubly-Pitched HiFlow™ Impellers – Open Impeller Design for High Viscosity Mixing Applications
The ProQuip Doubly-Pitched HiFlow impeller can be used in select high viscosity applications as an alternative to a double-helix impeller design.
The ProQuip Doubly-Pitched HiFlow impeller pumps in both directions and induces a vigorous top-to-bottom turnover of a vessel in a typical three impeller configuration without baffles. Water-like material circulates without excessive swirling. As viscosity increases, in applications like glue/adhesive manufacturing, top-to-bottom circulation is still maintained because the large diameter Double-Pitched HiFlow impeller creates a mixing zone essentially across the mixing tank diameter. This means viscous material cannot bypass the mixing zone because the entire diameter of the vessel is swept by the impeller. The Doubly-Pitched HiFlow impeller provides excellent agitation in the transition zone (Reynolds numbers in the range of 10-10,000) without requiring tank baffles.
The proprietary design of the ProQuip Doubly-Pitched HiFlow impeller results in a very low power demand. This makes it possible to use relatively large impellers without requiring excessive horsepower.
The following video demonstrates the mixing of the same high viscosity fluid used in the double-helix impeller video. The lab scale vessel is 13.25” diameter with three 12” diameter ProQuip Doubly-Pitched HiFlow impellers. The fluid viscosity is 10,000 cps.
The impellers are operating in a laminar flow regime. A colored dye is added to demonstrate the flow patterns and mixing of this high viscosity fluid. The impellers pump down in the center of the mixing vessel and up along its walls. The blend time for this high viscosity fluid using the Doubly-Pitched HiFlow impeller is also relatively short.
For More Information on High Viscosity Mixing Impellers
For more information about high viscosity mixing impellers, email email@example.com or call us at 330-468-1850. Other Industrial Mixing Basics blogs in our mixing impeller series include: