Determining the Required Net Positive Suction Head (NPSHr) in a Pump

PumpLinx effectively predicts NPSHr

PumpLinx effectively predicts NPSHr

Net Positive Suction Head, NPSH, is defined as the total fluid head at the inlet of a pump. The formula to calculate NPSH is:

Net Positive Suction Head

in which PT is inlet total pressure, Pv is vapor pressure of the fluid, r is density, and g is acceleration of gravity. Net Positive Suction Head required, NPSHr, is a very important parameter for centrifugal pumps. It is also referred to as NPSH3 per API 610, 11th ed. It determines when a pump will operate at three percent loss of head due to cavitation.

NPSHr Curve

NPSHr at different flow rates FEDSM2012-72282

 

PREDICTION: The Simerics Cavitation Module can be used effectively to determine NPSHr by running a series off virtual tests for the system of interest and determining when the performance exhibits a 3% head loss. For accurate results, the effect of vapor (Cavitation) and Non-Condensable Gases (NCGs) are both considered.

GENERATING AN NPSHr CURVE: An example of a curve generated using the technique presented in paper FEDSM2012-72282 is provided above, including comparison with data and illustrating the importance of modeling the effects of air content.

The complete ASME paper for outlining a procedure for accelerating this virtual testing process is available at “A Practical Approach to Speed Up NPSHr Prediction of Centrifugal Pumps Using CFD Cavitation Model” -FEDSM2012-72282.

Download our whitepaper, Predicting NPSHr, based on excerpts from this study.