Viscosity Correction

Most pump curves are developed with pure water, however, pumping a fluid more viscous than water will result in a reduction for pump performance - even if the fluid density is the same. AFT Fathom 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 account for this effect, correction factors referred to as CH, CQ and CE are defined. These correction factors are defined as:

To calculate the correction factors, it is required to enter the reference flow rate for corrections, as well as the rated speed for the pump. The reference flow rate for the correction factors can either be the calculated flow rate at the pump, or the flow rate at BEP can be used. If it is known, the flow rate at BEP should be used.

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 9.6.7-2015