Viscosity can be defined as the property of a fluid that resists the force tending to cause the fluid to flow. Basically, the viscosity is a measurement for how quickly a liquid flows. As you can imagine, trying to pump fluid much thicker than water can be challenging for many pumps, and outright impossible for others.
Animation of how the EDDY Pump outperforms centrifugal pumps when it comes to pumping high viscosity fluids.
Types of Viscosity Found in Fluids
In simple terms, liquid generally can be divided into two categories: Newtonian liquids and Non-Newtonian liquids. Non-Newtonian liquids can be further divided into two categories, depending on their properties: Thixotropic or Dilatant.
Liquids that exhibit constant viscosity regardless of shear rate or agitation. These fluids have a linear relationship between viscosity and shear stress and viscosity is only affected by temperature. Water or alcohol would be prime examples of Newtonian fluids.
Thixotropic or Shear Thinning
Liquids that exhibit reduced viscosity when agitated or mixed are referred to as shear thinning or thixotropic. Paint is a good example of a shear thinning liquid.
Dilatant or Shear Thickening
Liquids that exhibit increased viscosity when agitated or mixed are referred to as dilatant or shear thickening. Quicksand is a famous example of a dilatant.
The Difficulty Pumping High Viscosity
For high viscosity fluids, centrifugal pumps are not ideal because of the close critical tolerances and lack of ability to mix thixotropic materials to provide a shear thinning effect. Without this thinning effect, the viscosity is not naturally reduced by the action of the pump, causing the pump to require more and more power as the viscosity is increased.
As the viscosity increases, the pump performance needs to be adjusted to match the properties of the liquid and the resistance to shear. Pumping viscous liquid usually means a reduction in flow and head, as well as a significant increase in power needed to move the fluid.
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Typical Liquid Viscosities
|No. 4 fuel oil||12.6||15.7||80|
|SAE 10 oil||88||110||500|
|SAE 30 oil||352||440||2,000|
How to Determine the Right Pump for High Viscosity
First, you should try to determine the viscosity of the material you need to pump. The best way to accomplish this is to use a device called a viscometer. However, viscometers only measure viscosity under a single flow condition. For liquids with viscosities that can vary depending on flow, an instrument called a rheometer is used. Therefore, rheometer can be considered as a special type of viscometer.
Basically, these devices work by either moving them through a stationary fluid or by keeping the device stationary and running fluid past it. The drag caused by the relative motion of the fluid and a surface is a measure of the overall viscosity. Knowing the viscosity of the material to be pumped will greatly help in the overall pump selection process.
The EDDY Pump makes a great choice for pumping highly viscous material. The EDDY Pump’s geometric rotor acts as a mixer on thixotropic materials and provides a shear thinning effect enabling the pump to move high viscosity liquids much more efficiently than other pumps. The EDDY Pump’s ability to pump concentrated solids is perfect for moving viscous materials with less than 5% free liquid; an impossible task for traditional centrifugal pumps.
Choosing Pipeline Size
Viscosity is critical in determining the selection and sizing of piping, valves, and motors. Using a friction loss chart will detail friction loss data for a given flow rate, pipe size, and fluid viscosity, helping you select the right components for your job. This information combined with available viscosity data will allow a proper analysis of the fluid process system characteristics. Once the fluid process system has been designed and the pump operating parameters defined, the proper pipeline selection can be made. When handling viscous fluids, it can be tricky to determine how they behave. Experience is paramount, as there is no substitute for actually working with these materials out in the field and seeing how they operate.
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HD Pumps (Heavy Duty)
Pumping Viscous Red Mud – Highlights
This video shows how EDDY Pump performs when pumping high-solid red mud or bauxite which is abrasive, highly viscous, and corrosive.