NPSHr Definition and Assumption

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

6.5

is inlet total pressure, is vapor pressure of the fluid, is density, and is acceleration of gravity.

Net Positive Suction Head required () is a parameter determines, when a pump operates at three percent loss of head due to cavitation. This is the commonly used criterion for to pinpoint the limit for acceptable operation. At 3% head drop, a centrifugal pump experiences significant cavitation.

6.6

where, is inlet total pressure for 3% head loss.

Proposed Approach

Dr Hui Ding et al., proposed a practical approach to speed up prediction of centrifugal pump using cavitation model. For more information, refer “A Practical approach to speed up NPSH_R prediction of centrifugal pumps using CFD cavitation model-H.Ding, Y.Jiang et.al., FEDSM2012-72282.”

This approach can be used for the pump, where

6.7

6.8

where, is the change of pump head, is the difference of NPSH, and is the pump head.

Assumption

By default assumed 2% (by volume) of entrained air in the system. User can change the percentage of air content in the CFD model setup.