Viscosity Correction

Most pump curves are developed with pure water; however, pumping a fluid more viscous than water will result in a reduction of pump performance - even if the fluid reference density is the same as water. The Viscosity Correction feature employs the methods described in ANSI/HI 9.6.7-2021ANSI/HI Standard 9.6.7-2021, Rotodynamic Pumps - Guideline for Effects of Liquid Viscosity on Performance, 2021, published by Hydraulic Institute, 300 Interpace Parkway, Building A, 3rd Floor, Parsippany, New Jersey, USA. to correct for losses in performance due to viscosity.

Viscosity Corrections should only be used if the pump curve entered into the Pump Properties window is a water curve, since this is the only situation covered by ANSI/HI 9.6.7-2021. Viscosity Corrections will effectively transform a water pump curve into a viscous pump curve. If the manufacturer provides a pump curve for your working fluid at your desired viscosity, then it should be entered directly and the Viscosity Correction feature should remain disabled, otherwise the effects would be double counted. If the manufacturer provides a pump curve based on your same working fluid, but at a different viscosity, then the Viscosity Correction feature should still remain disabled because unfortunately that case falls outside the scope of the ANSI/HI 9.6.7-2021 standard.

Correction factors referred to as C_H (for head rise), C_Q (for volumetric flow), and C_E (for efficiency) are defined and can be displayed in the Pump Summary section of the Output:

To calculate the correction factors, the water BEP (head and flow at BEP) and rated pump speed are required.

• Assume Pump is Operating at BEP - This option is useful when the pump is in Sizing mode, and will assume that the head rise and flowrate calculated by the model are at BEP. This option is also useful when a water pump curve is entered but no efficiency data is present.

• Use Water BEP

  • From Pump Configuration - The water BEP flowrate can be determined from the pump curve data entered on the Pump Configuration window. This option will be disabled if efficiency data is not present.

  • User Specified - Alternatively, the user can directly specify the water BEP flowrate.

Scope of Correction

It is important to keep in mind that, like all mathematical models, this standard is not universally applicable. Below are the primary requirements:

• Single or multistage centrifugal pump

• Essentially radial discharge with specific speed under 3000 (US units)

• Newtonian Fluid

• Kinematic viscosity between 1 and 4000 cSt

For detailed information regarding these limitations and the application of the standard, please consult ANSI/HI 9.6.7-2021.