Pump is Viscosity Law Corrected: The performance curves for centrifugal pumps are generally based on testing with clean water. The pump performance therefore needs to be corrected if the fluid being pumped has a viscosity of 4.3 cSt or higher. Note, the value of 4.3 cSt is taken from the pump performance correction chart data detailed in the Hydraulic Institute Standards.
The reason for this correction is the pressure loss in the impeller and diffuser channels, the impeller friction and internal leakage losses depend to a large extent on the viscosity of the pumped liquid. Consequently, characteristics ascertained for water lose their validity when pumping liquid of higher viscosity, such as oil. In general, the higher the viscosity of the liquid compared to water, the greater the loss of delivery capacity and head for a given power input.
In general, the resultant de-rating of the pump head and flow rate may be relatively modest though the de-rating of the efficiency can be significant with consequences for motor size, switchgear and cabling if not taken into account.
FluidFlow will perform viscosity correction for the pump based on the Hydraulic Institute Standards.
Note, the correction applies only to centrifugal pumps delivering Newtonian fluids and the software will only apply the correction when a "Check-Mark" has been placed in the Global Settings Option titled "Include Viscosity Correction Factor for Centrifugal Pumps" (Figure 1) AND the flowing fluid viscosity exceeds 4.3 cSt.
Note, the Hydraulic Institute Standard correction methodology is valid between the viscosity range of 4.3 - 3300 cst which is the criteria which is implemented in FluidFlow.
This automatic correction will only occur if the option has been enabled from the Global Settings tab which can be accessed by selecting: Options | Calculation | Global Settings or alternatively, select "F2" & Global Settings (See Figure 1).